Just to reiterate here, multiplayer is the main reason some people play the game, so I really think the devs should look hard into these issues.
For a long time up to about two weeks ago, every time I played with my friend we had to give it a few tries before being able to join. Requests would time out, but after some tries it would eventually join. After the last update this changed, we have tried on several different days, and no matter how many times I attempt to join his game, it just doesn't work.
This last Friday, April 31st, for some reason I joined on first attempt and we were able to play without any issues. We tried again the next day and then again yesterday, on both occasions I kept trying to join his game for over half an hour. We tried lots of different suggestions from this thread, but nothing works.
Please look into this.