Ok doing some troubleshooting on my servers I have been able to replicate the weird behavior.

I started having issues as well after the 1.27 update. My symptoms are the access violation. As well, when this happens, players report no longer being able to join without crashing to the access violation error. What is interesting is I removed all mods from my server one by one to see if any one specific mod caused the issue, down to the point that it was just the Deer Isle map. It did not restore my ability to log back in. However, if I wipe the playerdb file and let players rejoin, it seems to behave fine for a short period of time. Upon slowly reintroducing mods, it seems to inevitably happen again. I would have anticipated the playerdb file updating as mods are removed and items are no longer in inventory but it's almost acting as if the playerdb is becoming corrupt. Most players state it works for a while and inevitably freezes and happens again. This happens to me on linux or on windows servers, as I am able to take the known broken playerdb, move it to my other server, and reproduce the issue, even with different mods.