Here is my first try. Its crashin.
I send you log and chrashlog.

Crashlog
https://pastebin.com/juiFaXnC

Latestlog
https://pastebin.com/AhPvPgkg

I have MorePlayerModels intalled, which is changing the render abit. I hope we can find the issue.

Edit: I tried without MPM and the issue was gone. Thats really sad because MPM is really needet in my pack. Their is a issue with rendering. For years i tried to fix it. This time their was some issues with rendering by pressing F5 to switch to third person view. I hope you can fix this issue.

I will send you a comment again after checking the bug. Perhaps, Can you give me the link to the your mode pack? I think I need your mode pack to check and fix bugs.

Ok. The pack is not uploadet. Do you need a list of my mods?

I need your mod list to reproduce the bug. Can you leave a comment here?

Ofc. Here:
https://pastebin.com/94CdewRj
MorePlayerModels is not in the list. But i want add if we can solve the issue.
https://www.curseforge.com/minecraft/mc-mods/more-player-models

Um.. There are so many mods, can you compress the mods file and send it to me? If you can send us the compressed file, please send it to 'Email Deleted'.

I send you my whole modpack, when i am at home tonight.

The file cannot be downloaded because it doesn't have permission. Can I change the file permissions to "open to anyone with the link'' in Google Drive?

Here is my modpack. The important files all their.
https://drive.google.com/drive/folders/1bFBqYAPQmmVDmaHHyK3E_K4tbfmeeIKM?usp=sharing

All the mods in the mods in the modpack works well with SM, just MPM not. :)

I am sry. This time it should work. If not i make a dropbox link.

https://drive.google.com/folderview?id=1smQgx17hZjv9YBEkehXMmkaQVBRQpgfi
or
https://drive.google.com/drive/folders/1bFBqYAPQmmVDmaHHyK3E_K4tbfmeeIKM?usp=sharing

Its not even needet. To reproduce the bug install SM with the APIs and install MorePlayerModels. Start the game and click F5 to change in third person view. The bug show up.

The conflict with the MorePlayerModels mod seems to be difficult to resolve in the current version. Since both SmartMoving and MorePlayerModels mods use Minecraft's ModelBiped class modified, it is difficult for both mods to work without conflicting unless one of the mods is newly developed from scratch. Therefore, it is recommended to select one of the two mods and put them in the mod pack.

And the phenomenon that the game crashes when pressing F5 after starting the game did not appear when I ran it using the rest of your mode except for MorePlayerModels mode. Please check if you misunderstood that you did not use MorePlayerModels mode and make a comment again after testing.

I figured out the same. Are you gonna investing in resolving this, to make MPM and SM compatible?

In the present version, modifying the code for compatibility with MPM is too hard for performance. Trying to use both modes as it is will be difficult unless the MPM creator modifies his mode and makes it compatible.

However, this problem will be solved automatically when redeveloping using the obfuscate library.

Nice solution. And the rest works like charm! The best way is to go with Obfuscate. I close the issue. Ty for your time and you work!