Nate I've found it would be this problem when using Path Contraint in a project. Using path contraint in 4.3 and export to 4.2 JSON, and it fail.

Thanks, we've fixed it in 4.3.19-beta!

Nate Thanks, now it can be imported to 4.2. But I lose all the Offset Value in Transform Constraint when open it in Spine 4.2

I don't see offsets being lost, but the constraint order and timelines are wrong. We've fixed this in 4.3.20-beta. Sorry for the trouble!

Ah I see now, thanks. Fixed in 4.3.21-beta!

Nate
Physics contraints Bug,
when build in 4.3,

And reimport to 4.2,

Mix Value is missing In Path Contraint:

JustHitIt Thanks for your report! Unfortunately, based on only two screenshots, it is unclear what the relationship is between the two skeletons. Are you saying that when you export the skeleton created in version 4.3.21 and import it into version 4.2, the Translate Y mix value changes?

When reporting a problem, it is always helpful to include the steps to reproduce it, as this allows us to quickly investigate the issue.

Misaki Yeah, the Translate Y mix Value will change

It is difficult to do anything with these reports. We have to try to recreate a project like what you have, export with 4.3, import with 4.2, then find the problem. When we try that and don't find a problem, we have to ask you for more information.

If you have a project that shows a problem, please just post the .spine with instructions on how to see the problem.

4.3 (left) when exported to 4.2 (right) doesn't show Y mix being lost. 4.3.21-beta

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seki Thank you for sending us the Spine project files! I believe I was able to reproduce the issue.
By the way, please note that the project you send us can always be simplified. In fact, I was able to understand the issue sufficiently even after deleting about 60% of the project you sent us.
Also, in cases like this where the bone movement itself is incorrect, you do not need to send us any images. It is sufficient to send only the .spine file.
We are currently investigating the issue and will respond to this thread as soon as we have more information.

Fixed in 4.3.24-beta!

The setup seems to be almost consistent, but there are still issues with the keyframes in the animation.

seki The text in Image 1 is incorrect; it should be 4.3.24

seki Thank you for reporting the issue. Using the project you provided earlier, I was able to reproduce the issue you mentioned, but I have not yet found a consistent way to reproduce it (i.e., a way to reproduce the issue when starting from a new project). I was unable to reproduce the issue by creating a new project, adding two bones, setting an IK constraint, adding a few constraint keys during animation, and exporting in 4.2 format. Therefore, I believe there may be another underlying factor, which I am currently investigating. I will let you know as soon as we find out something.

I think I figured out what's going on. It seems like the value of one IK constraint is being imported as the value of another IK constraint. So, when I tried to reproduce the issue in a new project, it didn't happen when I created only one IK constraint.
However, it seems that the naming of constraints is related to the confusion in importing, and I have encountered a phenomenon where changing the names results in different results. I am currently investigating why this is happening.

seki After completing some research, I have created an issue ticket here to fix this problem:
EsotericSoftware/spine-editor891
We apologize for the inconvenience, but please wait until we have resolved this issue.

Misaki I used the latest version 4.3 to try the previous operation, and a severe misalignment occurred. You can easily reproduce this issue using the previous project. Even in the 4.3.25 update, this problem still doesn't seem to be resolved — major errors already occur during the setup stage.