I’m not really sure if this counts as a bug or not, but the AI players really seem to have problems in the wet at Silverstone with fast cars - in particular, IndyCar and the Lotus E23. There seem to be several corners where they really struggle to stay on the track. Chapel and Stowe are both bad, but the worst by a mile seems to be Vale - they go off and don’t seem to understand what to do about the tyre barrier that is there now. Quite a few times, I have driven past three or four cars piled up together there trying to work out how to get back on the track.
Like I say, I don’t know if this is really a bug - peronsally speaking, I find it really funny, and also a cheap way to win a race at a canter! Doesn’t seem to happen at the other wet tracks that I’ve noticed, though.