The latest PTB builds are riddled with this error, when the player tries to attack an enemy city before you could choose to assault or continue to breach. Sometimes if you wait a few turns before attacking again, the problem fixes itself somehow, but sometimes it just breaks the game if you want a domination victory. Extremely annoying, and yea, sometimes even gamebreaking.
I would love to report this bug on the official bug report site, but it's even more bug riddled than the game...
#Unexpected Error when attacking a city
polar crown
real badger
Hello! Thanks for the report, we'll look into it asap! (TLPROD-56941)
polar crown
Hello! Thanks for the report, we'll look into it asap! (TLPROD-56941)
Hi! Thank you! It was such a blazing fast fix, that you rolled it out before your reply. 😄 Or it was already on your radar, or something, but today's patch seemingly fixed it. At least the one that's in the save (when trying to attack Sethy region with Opbot). I will report here, if this error happens again.