There is a weird bug in the latest update when view bobbing is turned on in which rendered block move along the player, when disabled the issue disappears, and has not caused any crashes. I'm currently using the latest forge version for 1.16.4, and using optifine G7, along several other mods. will try to replicate it later with just optifine and by itself.

If you need more information I'll do my best to provide it.

This issue has been marked as stale because it has been inactive for 3 weeks. It will be closed if it remains inactive for another 3 weeks.

This issue has been closed since it has been inactive for 3 weeks since it was marked as stale.

still happens without view bobbing

I just found out the issue, I had internal shaders on. Try turning your shaders off. I don't know how to fix it while it's on though.

Same issue here - Optifine + other mods, the whole world 'bobs' differently while walking with bobbing on.

Also having this issue, internal shaders is the problem as ItsMe129 said but if you are using it like I am for certain options then there's no fix that I found, messed around with settings and couldn't find anything to make it work.

I'm experiencing a similar problem, even with both internal shaders and view bobbing turned off.

The longer I leave it, the worse it gets too.