Sohm Al is the worst dungeon for me, I only lag on the last boss. I can't even see any of the ground AoEs half the time and I usually end up standing in all of them (except the comet things, I can see those!). I warn my parties about it every time, and sometimes I get kicked for "being lazy and not dodging". Sometimes other people can't see your lag, so if that guy said he was lagging bad he might have been telling the truth.