While on Overgrowth we started the exfil in construction. While waiting for the chopper the predator came for us we killed it and got the objective to protect the predator body, but when the helicopter left we got a left behind ending and no predator claim.
Update: It just happened again but on Backwater we killed the predator after we called in the chopper and got the hold out till the owlf gets there, but when the chopper exfil ends before the hold out timer ends we get left behind and the mission is over.