Hello! Based on the reports in this thread, I’m hazarding a guess this is a known issue where the server occasionally does not load everything up from the game database on startup. The items are not actually gone; they’re still in the database, but on each reboot/startup of the server, it is possible that some items may not load in.
We have a fix for this committed in an upcoming patch, likely due next week.
Edit 10/30/2021: The patch may not arrive this coming week. Will keep you posted.