Add me to the list of people that can't play. IF the map actually loads (about half the time after the loading screen I just see a backdrop with clouds/mountains and I have to exit) my character is just stuck in place for a minute, then I can slowly rubber band around the map. No mobs or doors spawn and I just see my team mates standing around losing health. I played perfectly fine until I got Keeper to lvl 6, but since then I haven't been able to play a single multiplayer match.
I solved my loading and multiplayer lag issues. Before getting Keeper to lvl 6, I hadn't added anything to the game's launch options under "Game Properties". The lag issues started after I unlocked the cutscene fps with "-GameTime.MaxSimFps 60 -GameTime.ForceSimRate 60+".
I removed "-GameTime.MaxSimFps 60 -GameTime.ForceSimRate 60+" from the launch options and now multiplayer works perfectly once again. No more weird loading and no more stuck character/rubberbanding. Maybe that'll help someone else too.