No specific repro steps but a report from another player we have filed a bug for in our database:

Hello, also received a turn pending error and it looked like the game got corrupted on the last turn (if not a few turns before as other players in the game were reporting odd things)- one example on the last turn: I had a City that had been captured by Empire B from Empire A earlier in the game. I (Empire C) had then captured it from Empire B but the city name was completely missing in the UI and I couldn't interact with it. Also the colours of various territories were wrong. 

For other players encountering infinite pending turns in multiplayer games, diagnostics logs and information on what you were doing in game at the time could help us. There are multiple things that can potentially cause an infinite pending turn, so the files can help us catch the other versions of infinite pending turns.