Fighting a vassal

[Don Andre]

Yesterday I declared war on a culture that was master to another. I also took the vassal's only city apparently. This somehow broke the vassal relationship and I was at peace with the culture despite having a city occupied. The city would remain in that state. I had to declare war again, but the culture doesn't have any possessions. So it's hard to win this war fast.

 

[Don Andre]

Again, really strange situation. A culture was fighting me + someone else. I took their only city and next turn they became vassal to the other culture and the city was theirs again. How can another player give back a city, that I have occupied??
Also, I attacked it again, strangely just taking it and it was under my occupation with 0 pop all the time and I couldn't make peace, because I was already at peace.
Only several turns later when I declared at the liege and won, I could get this city turned over to me.

There are really some corner cases that are buggy.

I am playing Stadia btw. Game started yesterday