I've come across an interesting situation in my 2nd playthrough: I was at war with the hittites, with 2 stacks of 4 scouts each in their territory, one of which was attacked by 2 warriors, and the battle didn't end in 5 rounds so it continued to the next turn. On the next turn, I had finished researching the tech and lets you reinforce your armies (Until then I didn't realize why I couldn't reinforce - this should also be better described so new players can understand it even without reading the info on tech which allows it - which is impossible in the neolithic era).
Now what happened is that I was prompted that I can reinforce my army, but when I try to do so it won't let me. I tried dragging the troops from the reinforcements tab to other tabs or to tiles on the map, but nothing worked. When I try to click on "end round" it says that it's not my round (because I was attacked I guess the hittities go first on the 2nd turn as well). But the game basically won't let me do anything including skipping the turn. I don't know where the save file is located so if anyone tell me where is the default folder for them in windows 10 I'd be happy to attach it in the next comment, but here is a screenshot which I hope helps explain my situation: