I didn't see anyone else stuck in the pits up to the point where you pitted in, so i can't take in consideration anything that happened before that.
What i can do is observe what happened when you did:
1- Pit slot was occupied but the other vehicles left on time so yours could get in
2- Warning message triggered and remained open for a long period, so there might be a logic issue here
3- The guy who pitted behind you was able to stop and leave while you were doing maintenance, but you never end up being released
4- All the vehicles from this point onward pit in and get stuck after the clear off from the pitcrew member
This makes me believe that none of the vehicles left the pit because they were waiting for your car to leave.
Back when we repro'ed the issue for the first time we were having similar scenario, car wouldn't pit in for some reason as if the slot was occupied, then we returned to pitbox and selected drive, at this point the vehicle would leave the garage and then forced into the pit-slot as if the request was pending but never got out.
Anyway, we'll be looking into it a bit further, there's definitely something odd going on here.