Training droids DD not working properly

Twice now I have run the training droid Datadisc in CQ with Leia (raddus drogan r2 and jyn) to try to get the sector 5 fracture feat and both times the disc worked well for about 4 minutes and then suddenly the enemy leader could die. The way it is written he shouldn’t die unless it is an instakill and there isn’t one available on this team. 

does the datadisc lose its effect at some point?