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.
from
Elemental Forums
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.