Buried items appear unburied after an unknown duration of time. Does not appear to be due to server resets - as I've had items stay buried for at least 3-4 days in a row.
This occurred most recently on the server (noted below) between 2/23/21 and 2/24/21.
While playing 1.10, I never encountered this, so I assume it may be a bug introduced with 1.11.
Update: This has happened two more times. So, now I've seen the bug occur 3x total.