I have similar issue. After Genesis update game is loading a lot of data, and after game start it is loading all for 5-10 minutes before disk usage goes down. I have a game on spinning rust, task manager shows that is all this loading time using ~60MB/s. During this loading period connecting to game will result in poor performance, not showing the map correctly or even not showing parts of the UI. Before Genesis season it was instant, I was able then to start a game and jump right in without an issue. Now i need to find something to do for that 5-10 minutes before game is playable.
Once it is loaded up, i can play normally and map change does not cause trouble.