I tried a reboot and it didn’t fix the issue. For some reason, every time I parked it at home and it sat overnight, the issue disappeared the next day. So, that may have been what happened since you parked it and your wife didn’t drive again until the next day.We have now and then gotten the "Cabin camera unavailable" message, which disappears after a moment and seems to have no impact.
Until Friday, that is, during a long drive home from the Bay Area. Friday, as others said above, when we engage Autopilot we are immediately in blue flashing mode. Disengage, try again, same thing. I waited a few hours and a charge stop, and same thing. After we got home, it belatedly dawned on us to reboot the computer. The next drive was this morning when my wife went out. She tried AP and it worked normally.
In short, a reboot seemed to fix it, which tends to confirm the suspicion of a software bug.
Side note: If indeed any of us do need the cabin camera replaced to actually fix this, it's kind of unfair for it to not be under warranty. For example, our car is four years old and over mileage for warranty. But we had no opportunity during the warranty to learn whether the cabin camera was functioning properly. Fair would be if the warranty clock for the cabin camera began when the software first started using it.
Granted, I tried the software reboot while driving, so I’m not sure if that makes any difference. Thanks for sharing your experience!