See #57 and #116.
I may have to create a workaround rather than fixing this directly if I can't figure it out.

I have not had an issue in the latest release. Specifically

If someone is having this issue on 1.16.5 and is willing, could I have a test world which consistently crashes with this issue?

I get the same error with my mod (https://github.com/nilsgawlik/gdmc_http_interface), which is on 1.16.4 right now, so it might be related. I have a world which crashes pretty consistently for me. Since this seems to be more of a Forge/Minecraft bug and tied to the world save, maybe that world save could still be useful to you?

Edit: Ah sorry, nevermind, I think I misunderstood. I just updated to 1.16.5, and don't get the bug anymore, either.