Okay, i've looked into it, can't reproduce it
.
Started a new game with the basic mod event, killed a civ via WB a round before the spawning, and the byzantines spawned just fine
.
Are python exceptions activated? If not, then do it please.
And i made a quick adjustment to ensure that the first mentioned city name will always be the capital, changed .py file attached.

Started a new game with the basic mod event, killed a civ via WB a round before the spawning, and the byzantines spawned just fine

Are python exceptions activated? If not, then do it please.
And i made a quick adjustment to ensure that the first mentioned city name will always be the capital, changed .py file attached.