I know very little about Ebikes : But it would seem obvious you have a Intermittent lost of connection somewhere . It makes no sense it works then doesn't then does : Sounds like either a faulty sensor or possibly wiring . It doesn't take Much.New update. I had a longer ride last night. On 28 mile The motor stopped responding and monitor was flashing “motor error”. I turned the motor off and then on and was able to finish the ride.
The issue with the power surging/dropping seems to be OK for now.
here is a pic.
Hope you get it figured out as I have the same Bike coming