The server cannot save chunks
What it looks like in your log
Failed to save chunk 12, -4
What causes it
Chunk writes are failing. In order of likelihood: disk full, file permissions, or a disk that is dying.
How to fix it
Check free disk space first, then file ownership on the world folder, then the disk health of the machine.
Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.
Check your own log