Bug: rendain invisible

i was playing the heliophage with galilea it was going fine. we got his shield gone(rendain visible) then the bosses we got them killed as well, BUT we had no lives left and i was benedict when rendain came back after the last boss and was invisible i had no clue where he was except the red marker when you aim at en enemy was my only clue where he was. it made us the mission fail

This happened to me last night with a 5 person team, we all died once he launched the backup team of super Thrall he calls in, we were a good team and knew it was coming but they were all over us.
Once we all died, only the Thrall where there, next thing you know we were transported to the final room.
The game ended with Success and we didn’t kill him. Everyone was like…What the heck just happened.