Affects Version/s: 1.16.1
Fix Version/s: None
Not sure on the exact cause of the freeze/crash, but it involves shulkers.
Try the following to reproduce:
1. Break the shulker while it is doing its closing animation
2. Have another player break the shulker while it is opened.
3. Have another player stand on top of the shulker while the shulker is being opened.
(Side note: players turn invisible if they stand on top of a shulker when it is opened.)