The player will take continuous damage similar to standing on a magma block while standing, crouching, or moving across the top of a chest.
The damage does not always start immediately, but placing blocks while standing or crouching on a chest seems to be a consistent way to trigger the bug. The damage does not stop until the player is no longer standing or crouching on top of a chest.
Linked issues
duplicates 1
Comments 3
So it does look to me like this is the same bug, as I have definitely confirmed that this happens at y=63. To add to MCPE-168518, the chests do not need to be double chests, and placing blocks is also a trigger. Additionally I have found that if the chests are supported by a solid block the damage does not trigger. The damage only happens if the chests are floating. This would indicate that the game thinks the player is repeatedly falling and hitting the chests, and support the fall damage theory of MCPE-168518.
In that case I'm going to resolve this as a duplicate of MCPE-168518. Thanks for confirming!
Possible duplicate of MCPE-168518, what are your Y coordinates?