Here's some videos of the post-patch 9 Silverstone Classic pit bug from last night's session. I'll add more as I receive them.
To the mods/devs: I don't think you'll reproduce this bug with just 2 or 3 of you in a MP race. I spent several hours last night trying to reproduce it with just two other racers and it wouldn't happen. We then abandoned the 'testing' phase and just invited our usual crew in (I think we had 10 humans + 4 AI) and ran a 'normal' ten-lap race with 15 mins quali, and the bug affected around half of the human payers as soon as they pitted. You'll need to take part in a well-populated MP race to see it for yourselves, I think. If you can't get into a public lobby (Joe Public tends to shy away from Silverstone Classic because of this issue) then you are welcome to join us one night if you want to run some detailed tests first-hand.
Here's a video from my PoV of the entire 15 min qualifying session, including the full pre-race menus and settings. I enter/exit the pits several times and 'return to pit box' many times with no issues (eg around 4:45). At around 10:45 I return to the pit box and monitor the other players, cycling through them several times where you can see a few of them are affected by the pit bug. Some of them have glitched displays, some have slo-mo/unresponsive controls, some of them have vibrating cars etc etc.
Anyway, hope this all helps, and many thanks to the rest of our group of racers for patiently contributing to something we all knew would turn into a flustercluck of crashed consoles.
(At least there didn't seem to be any mass disconnections...)