I was running running survival missions in railjack and noticed that some of the moa enemies were invisible and could only be damaged by melee attacks. All other attacks or abilities had no effect. I also noticed that the shield drones in railjack with the electric beams attack would randomly do nearly all my Grendel's health in a tick or two of damage. This last byg seems to happen regardless of railjack mission. The invisible moa bug seems to only happen in railjack survival and only during the survival portion of the mission, not any of the extra objectives.