Coliseum - DRYAX T7 can't be finished - HP Frozen

I cannot kill with 4 healthy Rebels level 80,80,80, and 79 and a borrowed level 80 a single dryad at 1% health. The total health bar at the top will NOT drop below 28% even though one is totally dead and the other on life support!

  I let it run on autobattle for over 15 minutes with stalled buggy progress or actually lack of progress in a de facto stalemate. 
  Finally the battle stopped, but not by me forfeiting. 
  Fix this please, I wasted attacks on this!!!