hmm what are all the mods you are running, and what other classes are involved in MP?

I have had no reports of lag or issues, its most likely a mod conflict, lets see if we can figure it out.

Sure thing! In order: LAO 2.0, Arkham's Armory, Awesome Classes Reborn, Torchlight II Essentials, Synergies.

My friend plays Necromancer. We've been playing for a while with no issues--it was only after the update that my game would freeze, and while his would continue on, all enemies would cease attacking him and just stand there. I'm the one hosting the game.

Thanks for your help!

well we have had MP issues with Essentials in the past with updates, read the synergies info, at the very bottom it states essentials can be finicky in MP. There is a Synergies friendly Essential MP release somewhere on the workshop. Other then that conflict I don't know what else in that list that could. maybe reroll your world, did you try that ( i did change population amounts on dungeons)