I would like to give you a quick update. I was able to reproduce the bug and to identify the problem.
The reproduction is: You play with at least two human players. Human player 1 ends his turn on the move. An event occurs and human player 2 starts it's turn at a city. Human player 2 is stuck now.
The bug appears with any event. There is no way to avoid that bug by adding computer players. The only chance to avoid it is to play without events of course.
I have created a fix and will release a new version the next days, after carefully testing the change.