Summary of the bug :
I just had the Liddo5 arena come up with destructibility turned off, resulting in a pointless romp that is, apparently still going on. Since there's 1 player romping around with AI still, the race isn't ending and anytime you try to join a race, that's the first one to come up, which kinda puts a stop to MP until that race closes.
Which version of Grip were you using :
When does this happen : Multiplayer race start
On which track did it happen : Liddo5 Arena
How often does this happen : So far only once.