try that, maybe somehow the bug can be removed somehow? Oh but remember to keep this savefile seperately (like the one where youre outside gesthra, maybe save it again in file 2 or something)
Hmm reading this now, that really seems to be a confusing bug... right now I have no clue what's causing this, as no event on the worldmap or in Gesthra should trigger a black screen upon entering a town and no one else seems to have had this bug so far either.
Do you have a specific weather condition in the game when you're trying to enter a place?