Every single time there’s an update for Shadowlands in the Battle.net launcher while you’re playing Shadowlands, the entire game will chug heavily and completely freeze after a bit.
I’m not sure why this happens, but it seems like every time I’ve got performance issues, it’s related to this as each and every time the chug starts, there’s an update.
Might just be because there are 10 million updates a day, but this is just what I’ve noticed. This same behaviour does not happen with WoW Classic.