I would say the one where Mobile Assault and Advanced emplacement regiment got added. Not only that both doctrines were beyond broken and OP (5 CP land matress destroying an OKW HQ in 1 barrage; free counter barrage vs mortars that attempted to destroy the almost unkillable emplacements), but it also removed veterancy from all units, caused the 100-man RE squad and 5x schreck /4x sweeper etc. bug on all squads after reinforcing.
And it bugged out the automatch map-pool as well. IIRC every 1v1 was played on Stalingrad, every 2v2 on Kharkov, every 3v3 on Rzhev Summer and every 4v4 on Steppes. No matter what maps you vetoed.
And it was during ESL as well
