When I was getting the warning messages, I pulled over, and inspected the cameras. The car was clean - and there didn't appear to be any thing on the camera lenses. Tried wiping them just with my thumb - didn't see anything - and the error didn't resolve.
Before starting the return trip - did a wiping pass with a microfiber cloth, noticed a little film coming off the side pillar glass, but nothing significant.
Unclear if NOAP coming back was due to the microfiber cleaning of the lenses - or if this was just a software glitch, that reset after the car was parked for a while (and likely went into and out of sleep mode).
If the issue didn't clear, I had planned to do a Power Off on the vehicle when I got home - in addition to doing another round of reboots for the console/dashboard processors - I've seen that resolve some issues in the past. But didn't have to get that far this time.