Sounds like the mechanic has messed with the torque sensor, this does not need to be touched when taking out the bike wheel. I changed tyres front and bike without problem. go back to the shop
My motor stopped working and the problem was with the brake. The handle was not coming back properly and read that i was breaking all the time. Unscrew, loosen, fixed
"I have the same problem. I take out the rear wheel and place a magnet over the torque sensor for a moment, and the motor in the front wheel start working for a few seconds and then stops
I think that the problem is the torque sensor (Is it a MTT sensor?)."