To get past Mission 12 bug, Train up your squad to level ~10+, do not use a sniper, use a short range gun/lmg on a tank or healer. Aim your gun vertically down CLOSE TO THE BODY, shooting or spamming controls if your game starts to freeze.
You should be able to finish the match in 3-10 minutes, try and go up against a squad that has tanker, engineer, gunslinger. If they have an explosive on the other team, restart it. It is RNG based took me ~12 attepmts but I managed to play a full game as a healer, aiming at the ground 2 captures myself, 3-1 score. Also use bison as SMG, I'd say its the best for completing the mission, with the lmg.
TLDR, Aim vertically down close range, DONT USE SNIPERS.
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