No, they had at least 2 other cities. I'll post a save if I can.
Edit:
Just reloaded the save...and I can capture the city without a problem! If I could have a guess, it's probably the "unidentified C++ exception" I had while waiting to spawn which caused the game to crash. It was definitely a stability-related exception, as the Python debugger made mention of a stability checking function.
Edit 2:
Playing a Byzantine game. It no longer feels like easy mode. It's actually quite challenging to defend all your borders. I've lost the Levant to the Sassanids and Constantinople got sacked, as a result of my meagre army getting annihilated outside of Edessa. I'll have to play more defensively next time.
I'm actually getting beat up very hard. Maybe that's why the Byzzies are a non-entity by the Arabs' time. Personally I like the challenge, it's more the AI I'm worrying about. Byzzies were OP a few versions ago, don't want to go back to that time.
Sassanid production seems pretty balanced as far as I can tell.
Byzantine Stability Bugs:
1. My economy is at +2 despite losing 2 GPT at 0% science.
2. I am stable despite a total balance of -1 +2 + 2 (the buggy economy value) - 7 -2 = -6
Further edit:
Can we disable cultural flipping? The only time that ever happens is when freshly-captured barbarian cities defect back to you, which is a silly bug caused by how "weak" barbarian culture is compared to civ culture.
Confirmed that after 270 BC, there is a significant slowdown between turns.