@paulp Thanks for the info! This seems to be confirming that the issue is due to special handling of undefined behaviour. We will continue our investigations.

@paulp We have just pushed a bugfix commit to the 4.2 branch which should fix this issue.
EsotericSoftware/spine-runtimes2574
You could integrate the shader changes of the above commit to your 4.1 package installation. Note that the commit fixes a second files, which is an include file used by the other URP 2D shader Universal Render Pipeline/2D/Spine/Sprite.

You can also find the modified file for your 4.1 URP package below:

Please let us know if this fixes the issue for you as well.

Issue ticket URL for later reference:
EsotericSoftware/spine-runtimes2574

@paulp Oh dear, very sorry to hear that the issue still persists on Intel UHD hardware!

Could you please have a try with this modified shader version and let us know whether it resolves the issue:

@paulp That's unfortunate indeed, thanks for the feedback. We will continue our investigations.

@paulp Unfortunately so far we were out of luck reproducing the issue on our end again. Nevertheless, below you can find a slightly modified version of the shader before I'm leaving the office for today, to hopefully speed up the process a little bit:

Tomorrow I will hopefully find more time, apologies for the inconvenience!

That's unfortunate, thanks very much for the quick feedback.

@paulp Bad to hear, thanks for the feedback.

To be sure we're on the same page: Are you testing with the exact same reproduction project that you sent us last, and play this in the Unity Editor play mode with active target being Playstation 4 or Playstation 5?

I'm asking to be sure you're not perhaps testing a more complex scene where other shaders are used, like additive or multiply shaders instead of the URP/2D/Spine/Skeleton Lit shader.

@paulp One more update, could you please test this version:

paulp Harald Thanks! Everything is fine on the test stage, there are no bugs.

Do you mean that with the last shader file that I shared three postings above it changed from having the issue to not having the issue any more? Or what exactly did you mean by "Everything is fine on the test stage, there are no bugs."? Where is the bug occurring now, using which target platform, only on the device or also when in the Unity Editor play mode?

paulp But in game we have this bug, maybe because we are also using Spine-SkeletonGraphic.shader?

This would have been my best guess so far, that the problem is fixed in the one shader above, and that there are other shaders in the scene which still have the issue and make everything look incorrect.

Thanks for the additional info.

paulp Yes, after your edits [..]

After which edits exactly? Only with the very last version that I mentioned above? Or with an earlier one, and if so, which one? This is important to know in order to be able to fix the issue in the SkeletonGraphic shader.