When returning to the Valkyrie at Comms-Plex, it is possible with ogryn to ult dash from the final gate to the spot where the valkyrie lands, have the valkyrie land on top the ogryn and get the ogryn stuck underneath the landing valkyrie, preventing the ogryn from boarding the valkyrie and ending the mission.
Despite best attempts enemies don’t target the ogryn either, preventing mission completion unless the offending player voluntarily leaves or is vote-kicked.