Mario I want to suggest simple temporary solution: add in Spine Editor (Desktop app) hint and basic name checking on the export screen.
Maybe Epic really willn't fix that very long time - but you can help Spine user right now. Better than nothing!

Oh, just got it now!
Can use 5.3, but every asset need unique name, like "s_boy.skel" with "a_boy.atlas".

Mario Hello!
Can You clear this point, please?
If I will upgrade my project and reimport just one using asset (standart spineboy) - it will worked? And how exactly I shouldn't name my assets for avoiding bugs?

Or latest Spine plugin just didn't worked correctly with 5.3 at all - and wise choise is just stand on 5.2?

(In my game I use FMOD and Spine - and first one is already updated, just waiting yours )

Hi!
I think, why Unreal runtime plugin is not available through native way of installing?
Compilation plugin after engine update is always a headache... If engine is working, then VS is broken, etc
FMOD, btw, always give working plugin without building need.

Yep, the issue was solved! Thank you, guys!

@Mario, are you there? I have changed topic for this bug.

UE4 Editor 4.26.2, the latest git version of runtime is still doesn't working.

I copy last message window there

The project could not be compiled. Would you like to open it in Visual Studio?

Running D:/Program Files/Epic Games/UE_4.26/Engine/Binaries/DotNET/UnrealBuildTool.exe Development Win64 -Project="C:/Users/pesez/Desktop/spine-ue4 4.26/SpineUE4.uproject" -TargetType=Editor -Progress -NoEngineChanges -NoHotReloadFromIDE
Creating makefile for SpineUE4Editor (no existing makefile)
@progress push 5%
Parsing headers for SpineUE4Editor
  Running UnrealHeaderTool "C:\Users\pesez\Desktop\spine-ue4 4.26\SpineUE4.uproject" "C:\Users\pesez\Desktop\spine-ue4 4.26\Intermediate\Build\Win64\SpineUE4Editor\Development\SpineUE4Editor.uhtmanifest" -LogCmds="loginit warning, logexit warning, logdatabase error" -Unattended -WarningsAsErrors -abslog="C:\Users\pesez\AppData\Local\UnrealBuildTool\Log_UHT.txt" -installed
Reflection code generated for SpineUE4Editor in 9,9828223 seconds
@progress pop
Building SpineUE4Editor...
Using Visual Studio 2019 14.29.30038 toolchain (C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30037) and Windows 10.0.19041.0 SDK (C:\Program Files (x86)\Windows Kits\10).
[Upgrade]
[Upgrade] Using backward-compatible build settings. The latest version of UE4 sets the following values by default, which may require code changes:
[Upgrade]     bLegacyPublicIncludePaths = false                 => Omits subfolders from public include paths to reduce compiler command line length. (Previously: true).
[Upgrade]     ShadowVariableWarningLevel = WarningLevel.Error   => Treats shadowed variable warnings as errors. (Previously: WarningLevel.Warning).
[Upgrade]     PCHUsage = PCHUsageMode.UseExplicitOrSharedPCHs   => Set in build.cs files to enables IWYU-style PCH model. See https://docs.unrealengine.com/en-US/Programming/BuildTools/UnrealBuildTool/IWYU/index.html. (Previously: PCHUsageMode.UseSharedPCHs).
[Upgrade] Suppress this message by setting 'DefaultBuildSettings = BuildSettingsVersion.V2;' in SpineUE4Editor.Target.cs, and explicitly overriding settings that differ from the new defaults.
[Upgrade]
Building 25 actions with 4 processes...
  @progress 'Compiling C++ source code...' 0%
  @progress 'Compiling C++ source code...' 4%
  [1/25] Default.rc2
  @progress 'Compiling C++ source code...' 8%
  [2/25] Default.rc2
  @progress 'Compiling C++ source code...' 12%
  [3/25] Default.rc2
  @progress 'Compiling C++ source code...' 16%
  [4/25] SharedPCH.UnrealEd.cpp
  @progress 'Compiling C++ source code...' 20%
  [5/25] SharedPCH.Engine.cpp
  @progress 'Compiling C++ source code...' 24%
  [6/25] PCH.SpineUE4.cpp
  @progress 'Compiling C++ source code...' 28%
  [7/25] SpineboyCppPawn.gen.cpp
  @progress 'Compiling C++ source code...' 32%
  [8/25] SpineUE4GameMode.gen.cpp
  @progress 'Compiling C++ source code...' 36%
  [9/25] MySceneComponent.gen.cpp
  @progress 'Compiling C++ source code...' 40%
  [10/25] SpineUE4GameMode.cpp
  @progress 'Compiling C++ source code...' 44%
  [11/25] SpineUE4.cpp
  @progress 'Compiling C++ source code...' 48%
  [12/25] SpineboyCppPawn.cpp
  @progress 'Compiling C++ source code...' 52%
  [13/25] SpineUE4.init.gen.cpp
  @progress 'Compiling C++ source code...' 56%
  [14/25] Module.SpinePlugin.cpp
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(47): error C4477: "printf": ? ??ப? ??ଠ??஢???? "%lu" ?ॡ????? ???㬥?? ⨯? "unsigned long", ?? ??ਠ⨢??? ???㬥?? "1" ????? ⨯ "size_t"
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(47): note: ४?????????? ?ᯮ?짮???? "%zu" ? ??ப? ??ଠ??஢????
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(48): error C4477: "printf": ? ??ப? ??ଠ??஢???? "%lu" ?ॡ????? ???㬥?? ⨯? "unsigned long", ?? ??ਠ⨢??? ???㬥?? "1" ????? ⨯ "size_t"
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(48): note: ४?????????? ?ᯮ?짮???? "%zu" ? ??ப? ??ଠ??஢????
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(70): error C4477: "printf": ? ??ப? ??ଠ??஢???? "%lu" ?ॡ????? ???㬥?? ⨯? "unsigned long", ?? ??ਠ⨢??? ???㬥?? "2" ????? ⨯ "size_t"
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(70): note: ४?????????? ?ᯮ?짮???? "%zu" ? ??ப? ??ଠ??஢????
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(118): error C4477: "printf": ? ??ப? ??ଠ??஢???? "%lu" ?ॡ????? ???㬥?? ⨯? "unsigned long", ?? ??ਠ⨢??? ???㬥?? "1" ????? ⨯ "size_t"
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(118): note: ४?????????? ?ᯮ?짮???? "%zu" ? ??ப? ??ଠ??஢????
  @progress 'Compiling C++ source code...' 60%
  [15/25] Module.SpineEditorPlugin.gen.cpp
  @progress 'Compiling C++ source code...' 64%
  [16/25] Module.SpineEditorPlugin.cpp
  @progress 'Compiling C++ source code...' 68%
  [17/25] UE4Editor-SpineEditorPlugin.lib
     ????????? ??????⥪? C:\Users\pesez\Desktop\spine-ue4 4.26\Plugins\SpinePlugin\Intermediate\Build\Win64\UE4Editor\Development\SpineEditorPlugin\UE4Editor-SpineEditorPlugin.lib ? ??ꥪ? C:\Users\pesez\Desktop\spine-ue4 4.26\Plugins\SpinePlugin\Intermediate\Build\Win64\UE4Editor\Development\SpineEditorPlugin\UE4Editor-SpineEditorPlugin.exp
  @progress 'Compiling C++ source code...' 72%
  [18/25] MySceneComponent.cpp
  @progress 'Compiling C++ source code...' 76%
  [19/25] UE4Editor-SpineUE4.lib
     ????????? ??????⥪? C:\Users\pesez\Desktop\spine-ue4 4.26\Intermediate\Build\Win64\UE4Editor\Development\SpineUE4\UE4Editor-SpineUE4.lib ? ??ꥪ? C:\Users\pesez\Desktop\spine-ue4 4.26\Intermediate\Build\Win64\UE4Editor\Development\SpineUE4\UE4Editor-SpineUE4.exp
  @progress 'Compiling C++ source code...' 80%
  [20/25] Module.SpinePlugin.gen.cpp

Nate wrote

@[삭제됨] I'm not sure what's going on there. Mario will be along soon to help out. You might want to create a new thread for your specific problem, so it doesn't get lost in the general 4.0 release discussion.

OK, i will wait for him in another topic at "Bugs" section.

So, I recommend all of UE Editor 4.26 users do not update for 4.0 right now, because it's have an issue with plugin's building stage

@Mario well, the error was changed

The project could not be compiled. Would you like to open it in Visual Studio?

Running D:/Program Files/Epic Games/UE_4.26/Engine/Binaries/DotNET/UnrealBuildTool.exe Development Win64 -Project="C:/Users/pesez/Desktop/spine-ue4 4.26/SpineUE4.uproject" -TargetType=Editor -Progress -NoEngineChanges -NoHotReloadFromIDE
Creating makefile for SpineUE4Editor (no existing makefile)
@progress push 5%
Parsing headers for SpineUE4Editor
  Running UnrealHeaderTool "C:\Users\pesez\Desktop\spine-ue4 4.26\SpineUE4.uproject" "C:\Users\pesez\Desktop\spine-ue4 4.26\Intermediate\Build\Win64\SpineUE4Editor\Development\SpineUE4Editor.uhtmanifest" -LogCmds="loginit warning, logexit warning, logdatabase error" -Unattended -WarningsAsErrors -abslog="C:\Users\pesez\AppData\Local\UnrealBuildTool\Log_UHT.txt" -installed
Reflection code generated for SpineUE4Editor in 9,9828223 seconds
@progress pop
Building SpineUE4Editor...
Using Visual Studio 2019 14.29.30038 toolchain (C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30037) and Windows 10.0.19041.0 SDK (C:\Program Files (x86)\Windows Kits\10).
[Upgrade]
[Upgrade] Using backward-compatible build settings. The latest version of UE4 sets the following values by default, which may require code changes:
[Upgrade]     bLegacyPublicIncludePaths = false                 => Omits subfolders from public include paths to reduce compiler command line length. (Previously: true).
[Upgrade]     ShadowVariableWarningLevel = WarningLevel.Error   => Treats shadowed variable warnings as errors. (Previously: WarningLevel.Warning).
[Upgrade]     PCHUsage = PCHUsageMode.UseExplicitOrSharedPCHs   => Set in build.cs files to enables IWYU-style PCH model. See https://docs.unrealengine.com/en-US/Programming/BuildTools/UnrealBuildTool/IWYU/index.html. (Previously: PCHUsageMode.UseSharedPCHs).
[Upgrade] Suppress this message by setting 'DefaultBuildSettings = BuildSettingsVersion.V2;' in SpineUE4Editor.Target.cs, and explicitly overriding settings that differ from the new defaults.
[Upgrade]
Building 25 actions with 4 processes...
  @progress 'Compiling C++ source code...' 0%
  @progress 'Compiling C++ source code...' 4%
  [1/25] Default.rc2
  @progress 'Compiling C++ source code...' 8%
  [2/25] Default.rc2
  @progress 'Compiling C++ source code...' 12%
  [3/25] Default.rc2
  @progress 'Compiling C++ source code...' 16%
  [4/25] SharedPCH.UnrealEd.cpp
  @progress 'Compiling C++ source code...' 20%
  [5/25] SharedPCH.Engine.cpp
  @progress 'Compiling C++ source code...' 24%
  [6/25] PCH.SpineUE4.cpp
  @progress 'Compiling C++ source code...' 28%
  [7/25] SpineboyCppPawn.gen.cpp
  @progress 'Compiling C++ source code...' 32%
  [8/25] SpineUE4GameMode.gen.cpp
  @progress 'Compiling C++ source code...' 36%
  [9/25] MySceneComponent.gen.cpp
  @progress 'Compiling C++ source code...' 40%
  [10/25] SpineUE4GameMode.cpp
  @progress 'Compiling C++ source code...' 44%
  [11/25] SpineUE4.cpp
  @progress 'Compiling C++ source code...' 48%
  [12/25] SpineboyCppPawn.cpp
  @progress 'Compiling C++ source code...' 52%
  [13/25] SpineUE4.init.gen.cpp
  @progress 'Compiling C++ source code...' 56%
  [14/25] Module.SpinePlugin.cpp
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(47): error C4477: "printf": ? ??ப? ??ଠ??஢???? "%lu" ?ॡ????? ???㬥?? ⨯? "unsigned long", ?? ??ਠ⨢??? ???㬥?? "1" ????? ⨯ "size_t"
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(47): note: ४?????????? ?ᯮ?짮???? "%zu" ? ??ப? ??ଠ??஢????
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(48): error C4477: "printf": ? ??ப? ??ଠ??஢???? "%lu" ?ॡ????? ???㬥?? ⨯? "unsigned long", ?? ??ਠ⨢??? ???㬥?? "1" ????? ⨯ "size_t"
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(48): note: ४?????????? ?ᯮ?짮???? "%zu" ? ??ப? ??ଠ??஢????
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(70): error C4477: "printf": ? ??ப? ??ଠ??஢???? "%lu" ?ॡ????? ???㬥?? ⨯? "unsigned long", ?? ??ਠ⨢??? ???㬥?? "2" ????? ⨯ "size_t"
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(70): note: ४?????????? ?ᯮ?짮???? "%zu" ? ??ப? ??ଠ??஢????
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(118): error C4477: "printf": ? ??ப? ??ଠ??஢???? "%lu" ?ॡ????? ???㬥?? ⨯? "unsigned long", ?? ??ਠ⨢??? ???㬥?? "1" ????? ⨯ "size_t"
  C:/Users/pesez/Desktop/spine-ue4 4.26/Plugins/SpinePlugin/Source/SpinePlugin/Public/spine-cpp/src/spine/Log.cpp(118): note: ४?????????? ?ᯮ?짮???? "%zu" ? ??ப? ??ଠ??஢????
  @progress 'Compiling C++ source code...' 60%
  [15/25] Module.SpineEditorPlugin.gen.cpp
  @progress 'Compiling C++ source code...' 64%
  [16/25] Module.SpineEditorPlugin.cpp
  @progress 'Compiling C++ source code...' 68%
  [17/25] UE4Editor-SpineEditorPlugin.lib
     ????????? ??????⥪? C:\Users\pesez\Desktop\spine-ue4 4.26\Plugins\SpinePlugin\Intermediate\Build\Win64\UE4Editor\Development\SpineEditorPlugin\UE4Editor-SpineEditorPlugin.lib ? ??ꥪ? C:\Users\pesez\Desktop\spine-ue4 4.26\Plugins\SpinePlugin\Intermediate\Build\Win64\UE4Editor\Development\SpineEditorPlugin\UE4Editor-SpineEditorPlugin.exp
  @progress 'Compiling C++ source code...' 72%
  [18/25] MySceneComponent.cpp
  @progress 'Compiling C++ source code...' 76%
  [19/25] UE4Editor-SpineUE4.lib
     ????????? ??????⥪? C:\Users\pesez\Desktop\spine-ue4 4.26\Intermediate\Build\Win64\UE4Editor\Development\SpineUE4\UE4Editor-SpineUE4.lib ? ??ꥪ? C:\Users\pesez\Desktop\spine-ue4 4.26\Intermediate\Build\Win64\UE4Editor\Development\SpineUE4\UE4Editor-SpineUE4.exp
  @progress 'Compiling C++ source code...' 80%
  [20/25] Module.SpinePlugin.gen.cpp

I'm absolutely lost. New plugin's version doesn't build at all.

It seems not depend where you are trying to use runtime: example from git "spine-ue4" or your project. There's only one error:

Running D:/Program Files/Epic Games/UE_4.26/Engine/Binaries/DotNET/UnrealBuildTool.exe Development Win64 -Project="D:/Unreal Projects/spine-ue4 4.26 - 2/SpineUE4.uproject" -TargetType=Editor -Progress -NoEngineChanges -NoHotReloadFromIDE
Creating makefile for SpineUE4Editor (no existing makefile)
@progress push 5%
Parsing headers for SpineUE4Editor
Running UnrealHeaderTool "D:\Unreal Projects\spine-ue4 4.26 - 2\SpineUE4.uproject" "D:\Unreal Projects\spine-ue4 4.26 - 2\Intermediate\Build\Win64\SpineUE4Editor\Development\SpineUE4Editor.uhtmanifest" -LogCmds="loginit warning, logexit warning, logdatabase error" -Unattended -WarningsAsErrors -abslog="C:\Users\pesez\AppData\Local\UnrealBuildTool\Log_UHT.txt" -installed
D:/Unreal Projects/spine-ue4 4.26 - 2/Source/SpineUE4/MySceneComponent.h(8): Error: #include found after .generated.h file - the .generated.h file should always be the last #include in a header

What am I doing wrong? There was not with previous runtime version - plugin was successfuly builded before. Version of UE doesn't change - it's 4.26.2