Tested online for up to 6 players and this is what I have experienced.
The joining lag issue I believe have been greatly reduced. I was riding at washington when somebody joined the game almost never frost. Another rider joined and it did freeze a bit but unlike before that it freezes for like 4 seconds. Clearly it has improved. Now, the problem is that, the game now crashes more often than in B7 when somebody joins. So it's either somebody can join without freezes while you are on track or the game crashes. When I tried to join every after crash, the game just won't let me join back to the same server at all, It just closes the game without any error. So I tried another server and it was great to see another rider joined in that my game never frost. But when there was another player who joined in, game crashes.
Thank you!
idk if this will be of help or not, but when you try to join the server after your game crashes, if you are able to click cancel before your game crashes when joining then you should be good. i noticed(on my server) that when i connect and my game crashes, i have to join the server and click cancel, and then i can rejoin without issues