It’s proximity based. I can clear the error just by getting the bottom of the vacuum close enough to a flat surface, even a wall (so not a tilt sensor). It’s probably dual-purposing those cliff sensors. I assume you made sure they are completely clean. I’ve not had to do anything special so far besides a quick vacuum off, the anti-static spray I use (Reztore ESD Surface & Mat Cleaner) helps a lot.
According to a vacuum robot overview that I’ve found, the Wyze Robot has 4 IR drop sensors.
I still need to validate if the two near the wheels are specifically for the on-ground/level detection. (2023-04-30)