Hi, samdg. I had the same problem with the Open Sea mod activated. Kindly go to "new-horizons/PROGRAM/InternalSettings.h" and make sure OPEN_SEA_MOD is at 0. If you play on Iron Man difficulty, this will be automatically activated.
I apologize. I'll get back to you once I find anything. Meanwhile, please consider joining Buccaneers Reef discord channel: https://discord.gg/Ps3zMtP
ChezJFrey and other people who might be able to help are online and active on there.