I recently started getting some A-01 errors and saw from the manual that this occurs when the fan blower rpm drops under 400 which was happening at F4 and below. The first recommendation is to recalibrate your fan so I did that but it stayed stuck on F2 and the rpm never got over ~600 during calibration. I played around with it more today and it looks like my issue might have been that I did not have the fan calibration mode set to bl-16 which is the setting for the old motor (including my v1.5 bullet). Once I changed that calibration was able to hit a full range of rpms so I think I’m good now.
I don’t know why I just started getting the rpm errors and if I was previously miscalibrated but it does seem that getting that setting correctly during fan calibration is very important and it would be nice if the manual mentions it as one of the first steps.