For some reason, the client crashes, whenever I build a contraption in my modded server, but the server doesn't crash. The client doesn't crash instantly, but only after some time. After that time, whenever you try to log in again, the client crashes. Deleting the chunks, where the contraption is, fixes the problem. The contraption was pretty simple, it included a waterwheel, vertical gearboxes and a mechanical press with a basin. Image of something similar:

Crash report:
crash-2021-02-23_20.09.06-client.txt

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.

Try to update Optifine to version 1.16.5_HD_U_G6. It works with 1.16.5 and 1.16.4

Im getting the same issue with my server just hoping a fix gets put out soon