Have now unsubbed from Where's mu Beefalo, just turning off didn't fix it (my bad). Game runs fine now. Server files included for curiosity, server_log_2022-03-24-22-53-51.txt server_log_2022-03-24-22-53-51.txt
Tested hosting on two local servers, adjoining biome type doesn't have an effect, issue appears with and without mods. Approaching the swamp biome causes the game to crash. Loading the game and hosting the server, and walking away from the swamp allows it to continue running.