My attempt to beat alternate endings has failed.

During End of the Line where you must kill the RR, Deacon is always immune to damage and I cannot kill him or proceed with the mission.


I tried reloading and dissmissing him; sending him to a settlement, tried letting him just go back to the RR HQ. All with the same result.


I cannot beat the game without killing him. Anyone else have this issue and were able to solve it?