Another player just entered a game (not his turn) and changed battle orders. I did not know about it. Got "Target has changed" when i tried to attack. When I updated page, it was another unit on top and still not possible to attack. The unit moves as usual, but nothing happens. When it stands next to it, it just stops.
Game 39930, green units in the north, between a move temple (to the right), a black city (to the left) and below a razed city. In one of those paths through the mountains.
Edit:
My team mate just killed him. NN to check for the bug. Will try to recreate in a 1vs1 vs myself instead!