Hello @AnkerOfficial, Looks like this fault reoccurred. Here are the details:
1) I flipped the unit over and masked the drop-sensors with blue painter's masking tape.
2) I powered on the unit and set it to autoclean. It tripped the main brush stuck fault (solid red light, 4-beeps)
3) I powered off, removed the main brush, powered on, and started it again. Same main brush stuck fault.
4) I power cycled it again and set it to AutoClean, this time, spinning the main brush attachment point with a screwdriver with the intent to spin any possible encoder inside the mechanism. No luck. Same quad-beep fault.
In all instances, the main brush appears to never be energized. The vacuum starts up and a side brush spins (yes, only one), but the main brush never even quivers. The time between pushing the autoclean button and the fault is ~1-second.
A side note. after I got it working on 1-June, I started tripping side-brush faults, even though they had just been cleaned. No idea why this does not appear any more. Perhaps its the order of fault detection in your software where main brush is checked first.