Connection Issues With "Excellent" Connection

I played a custom before and everything went fine not even a high ping, then i play a normal and i cant even connect. Says im crashing and to look if u have a firewall up. This has already happened 3 other times and this is the 4th and it all resulted in games i couldnt rejoin so it said "Leave" on my match history so now I just keep trying to recconect with no results except "your game has crashed" and i really do not wanna get banned for this. Any help or tips