I attempted to help some lower level players complete the mission "Checkmate" last night. We got to the compound and there were zero enemies guarding the communications building. Weird but we carried on. After the cutscene we started fighting Walker which is when things were FUBAR. For a start Walker's Wolf backup was stuck outside the comms room and we couldn't eliminate them. They, for some reason, could still fire at us. On top of that the drones that provide Walker's shield disappeared completely. The end result being that Walker was immune to everything we threw at him as there was no way to take down the shield as the drones were invisible.