Game Performance

I was in a group of about 38 players trying to beat Omen for the first time on this server, and everything was fine until everyone started attacking after the tank built some aggro. The game started running at 1-2 FPS, and I didn't realize what was happening until the beast was dead. The only mods I had installed at the time were Nampower, Vanilla Fixes and UnitXp. I also had dxvk for the HD patches, but I wasn't using them at the time for reasons beyond my control. Do you think it could have the opposite effect without the HD patches? Any suggestions, or does anyone have any idea what might have happened?