Server crash: models/error.mdl couldn't be loaded

Daily, sometimes twice a day, my Garry’s Mod server will crash with

After the server goes back up, that exact model will load fine.

The NFO support people are pretty much stumped, any suggestions?

No lua errors, nothing. That’s the only error within the last 5 lines of the server log

If you have access, run an update on the server and it should update broken/missing files.
If not, ask NFO to update it for you.