林汤圆 Unfortunately I did not get a good understanding of what you were trying to do from your description. However, if by '当我用网格把一个A贴图分成A1和A2两个部分' you mean that you have created mesh attachment A2 as well as mesh attachment A1 which references texture A, then the same texture will not be output twice on the texture atlas page, so the result should be correct.
As it is difficult to understand the situation in writing, please send us your Spine project files via email so we can see what the problem is: contact@esotericsoftware.com
Please include the URL of this forum thread in the email so we know the context. Then we can take a look at what's wrong.

林汤圆 Thank you for sending us a Spine project that can reproduce the problem! Certainly this appears to be a bug and I will create an issue to fix this problem.

@林汤圆 I have created an issue to fix this problem: EsotericSoftware/spine-editor849
Actually, we had received some reports that some image areas could be lost when using polygon packing if there were multiple mesh attachments referencing the same image and trimming a specific area using the mesh hull, but we had not found it possible to reproduce this simplified case, so the reproduction project you sent us was very helpful. Unfortunately, we cannot say when this will be fixed, so until we can fix it, we would appreciate it if you could modify the image paths so that they refer to separate images rather than the same image.