Any specifics to look at? I know vanilla movement is intercepted, perhaps the solution is as easy as adding an if statement that allows vanilla to reassert itself if the person is in the air with an elytra?

@LimerenceCantCode

Oh, I've never thought of your solution, but I think it's good.

It would be great if you could solve this bug and then make a Pull Request to contribute!

I already know about this error. This is a problem that occurs because the existing source code does not compatible the 1.12.2 version. The existing source code is too complex, and you need to redevelop the mode with Obfuscate to fix this problem.