Update: I tried creating a new install using the May 2018 installer and not using any updates, and it did the same - crashed after the scene with Christopher Backer in the Tortuga outskirts. And I
know I've played "Bartolomeu" to conclusion more recently than May 2018.
There are a few other places where I've noticed the game has a tendency to crash. Port Royale town hall during "Tales of a Sea Hawk", Havana vice-admiral's residence during "Assassin", and Port Royale church when reporting back after a quest. If I remember, I always save game if I'm in one of these places on quest business. Though I don't remember doing so, I probably did the same at Tortuga town outskirts when I last successfully played "Bartolomeu". If the game crashes, I reload the savegame and try again.
So then I tried the current install again, loaded
@Nenketsu's savegame, tried to go back into town - and this time it worked.
I've no idea what causes these crashes - perhaps the memory leaks contribute, but that's just a guess based on a lack of evidence for anything else. In any case,
@Nenketsu, try resetting the PC, start PoTC again, load up the savegame - and keep trying until you make it back to town.