This also happened to me numerous times over the last couple CvC's, the little tent on the bottom of the screen does not appear at the bottom of the screen to give you the option to leave the tile after an attack so you go into the lair screen to hit the red cancel button instead but that also does not work. The only option is to relog the game then the tent will appear and you can recall your troops. Most times i was quick enough but I finally got smashed hard because of the long delay. If it was a one off i wouldn't be concerned but in the last couple weeks it has happened at least a dozen times making for some tense moments