A sent 3 assassins to a mission and the the timer hit 00:00:00 it got stuck there. I restarted the app and the mission was ready to run but it said that the assassins was on a mission. Now they have a clock on them and can't be used for ever. You should have a check to see if assassins is in a mission while all missions are completed/ready and make sure they can be used again! Can't be that hard.

It is on Android btw.