It seems if you get an attack on one of your cities and it doesn't happen, you can prevent the game from getting stuck by saving and loading the save.
I think loading latest autosave might work too.
Note: there is still something weird when more than one army attack on the one turn. It is either they are from the same square, or when you get a level-up after the first battle on an AI turn that the second attack doesn't materialise.