@KorNoob Thanks for your detailed writeup. According to the error message and stack trace, it might likely be that the initial frame of the new SkeletonDataAsset is not showing anything, which will might lead to the required render texture height being 0. Could you please confirm whether this might be the case?

Could you also please send us a minimal Unity project which still demonstrates this issue? You can send it to contact@esotericsoftware.com, briefly mentioning this forum thread URL so that we know the context. Then we can have a look at what's going wrong.

@KorNoob Thanks, looking forward to the reproduction project.

KorNoob Thank you for sending us a repro project! I am afraid to say but that the data you sent us was much larger than we would generally expect. (677MB)
When you send your Unity project to someone, it is enough to have Assets, Packages, and ProjectSettings in most cases, so if there is a next time, we would appreciate it if you could delete the Libarary folder and other unnecessary files before sending them to us.
We will look into this and let you know if we find anything.

@KorNoob Thanks for sending the package. Please note that we requested a minimal Unity project which still demonstrates this issue, but your project and example scene contains a network manager with all kinds of unrelated things. Please understand that we don't have the time to debug your net-code for potential issues there.

You need to boil down the issue to a reproduction scene which just uses one or two scripts which re-create the whole problem, with as few lines of code as possible, definitely without any network code involved. Then we can have a look at what's going wrong.

@KorNoob For example, the reproduction example script would setup the skeleton with one SkeletonDataAsset assigned, then e.g. set fade-out opacity accordingly, then assigns a different SkeletonDataAsset in a way which lets the issue occur.

@KorNoob Thanks for your understanding. Looking forward to the updated package.

KorNoob 마지막에 달아주신 답변내용은 제가 SkeletonDataAsset을 교체할때 잘못된 방법을 사용한것이라고 해석하면 될까요? 번역기가 정확하게 번역하지못해서 이해하기가 조금 어렵습니다.

No, I didn't mean that you used the wrong method, I just described that your reproduction project example scene should use just a simple script, as simple as possible. It was not intended to say that some method call is wrong in your code. It should just be minimal, without any unnecessary layers around it.

@KorNoob We just released a bugfix for this issue, both for SkeletonRenderTexture and SkeletonGraphicRenderTexture.

A new spine-unity unitypackage is available for download:
https://esotericsoftware.com/spine-unity-download
Please let us know if this fixes the issue for you as well. Thanks again for reporting!

Issue ticket URL for later reference:
EsotericSoftware/spine-runtimes2529

@KorNoob Very glad to hear it resolved the issue, thanks again for reporting!