I experienced this problem 2 days ago and it's happening again. It just solved by itself at first time but now I'm not sure when it will be. I've also read all the messages in the mailbox. ...
Ideas
The type of internet traffic used by multiplayer games is unique. Do you play any other multiplayer games? Are they working? I ask because there are confusing issues in the area of wi-fi security currently....so wifi routers are getting more security updates than usual. Also, wifi routers don't last forever and they sometimes fade away so slowly that you don't notice the decreasing performance.
I use LAN and have zero issue elsewhere. Also my pc environment have never changed since I played this game but suddenly got this problem.