Belmorne's pass mission doesn't end if enemy unit is in arena

I was playing Belmorne's pass mission, had complete map control and no enemies passed,

New enemies kept spawning but got killed constantly but the mission didn't end and didn't state win condition except that 0/10 enemies passed.

I had an enemy unit in my arena that was still alive and after about 1 1/2 hours I finally decided to kill that unit to try and progress and that did trigger the win.

Please consider stating that all enemy units must be killed as a win condition or at least don't count enemies that is in Arena or prison etc