The attached clip from social media taken in at least 1.21 (as proven by the Days Played counter) demonstrates a random damage bug when stepping inside broken blocks. My guess is that the game server believes there are still blocks where the player is standing, so it applies either suffocation or fall damage (damage source is unclear).

To Reproduce

1. Set render distance to maximum (to increase potential lag)
2. Enable autosave icon (to see when the game is saving, which causes lag)
3. Create new world with simulation distance set to maximum (to increase potential lag)
4. Break a tree while the world is both loading chunks and autosaving
5. Step inside the broken tree trunk blocks
6. Observe the player taking random suffocation/fall damage
7. Observe the bubbles bar appearing

Expected Results

The player does not take damage while standing in air blocks.

Observed Results

The player takes random unfair damage due to either suffocation or fall damage (damage source is unclear in the video).