phtcloud We apologize for the inconvenience. We have confirmed that there is an issue where Spine projects created with 4.2.43 cannot be opened with 4.3.39-beta. (They could be opened with 4.3.38-beta, so it appears that the issue was caused by this patch version.)
We will fix it as soon as possible.

Regarding the second question, I believe that the second issue is most likely not a bug. Currently, when attempting to save a 4.2 Spine project in 4.3-beta, the following warning is displayed:


The first warning is about trying to save a project created in an older version in a newer version. The second warning is to inform you that since 4.3 is still in beta, the runtime may not yet support it. This warning was added because many users encountered errors when trying to play skeleton data files exported from 4.3-beta using a runtime that had not yet been updated to support 4.3-beta.

phtcloud Although it has not been released yet, the issue where the project could not be opened in 4.3.39-beta has been fixed in 4.3.40-beta. Thank you very much for reporting this issue!