So I just played Lost to the Past in Sukhotai. When it completed, it put the brick wall back up that leads you inside, so I can't leave. It has also put every item I've collected back in the world, so I now have two copies of the relic found there. If I roll back to further saves, that latter bug is still present.

Seems to be somewhat to do with a desync between steam cloud and local saves. But both the local and cloud saves had this problem.

No idea what to do, can't progress. 36 hours in, so I'd rather not restart the whole game, especially since it might happen again.