What were you doing before bug occurred: I joined the server while in the middle of the Fort Talos mission. I killed the dude, fled, sailed to Ravenna, and none of the towns were loaded. Most of the terrain was loaded, but there was one underwater part (which I failed to record) where I swam to and another guy said I was phasing through the map and accused me of hacking.
Steps to reproduce:
have shit internet
Join the game in the middle of the Fort Talos mission.
Finish the mission, go to Ravenna.
Kill everyone with your new, possibly irreplicable, phase-shifting powers.
Since you mention an underwater part, perhaps Ravenna was being hit by a tidal wave prior to when you got their and it destroyed all the houses. But I have also heard of people failing to load in islands so perhaps it could be similar to that.
I was the only one that couldn’t see the buildings and terrain parts. To other players, I was noclipping through solid objects. I abused this to run away from a max-level RKer and they accused me of hacking (which I probably would have done as well).