So I had only about 500 turns. Saved after opening the boss door and such. Was going to go back and clean up after the credits rolled but then I get stopped by... well it's probably a spoiler to say.

Was there something that triggered this?

I did a few rounds of unsaved scouting but that couldn't have impacted it could it?

Even if the curse reapplied I should have had a few hundred more turns left.