Thank you both very much for your input, and especially AEO for the testing. May I inquire - what is odd about the forest on the server side?
Edit: Bizarrely, I have now managed to connect with my debug build and neither it nor the server have crashed. It is now June 2:01.
Edit 2: To confirm, the server is now back up. However, I seem to have noticed a pattern. The ability to connect and remain connected appears to occur after connecting to the troubled game and then disconnecting again before getting to the point where it crashes. Last night, while testing with a local server, I accidentally connected to the Bridgewater-Brunel server for a very short time, but disconnected before reaching the month end. I seem to remember something similar happening before the bug mysteriously disappeared last time. That suggests some issue with the save/load code (which might also explain why the viewport has ended up in the middle of the sea on loading rather than next to the island with the name of the server on it. Quite where this problem is, however, is a mystery to me as yet.