computer problem

Hi, I bought Trek Powerfly 7 half a year ago. And now I have problem with speed on cycle computer. If I ride around 20 km/h, the speed on computer starts jumping around - 24, 18, 23 etc. But in real the speed is still the same 20km/h. Diagnostic looks OK. Does anyone had some issue? Thank...

I recently bought a second hand 2017 volt bike mariner and it was fine for the first month but I woke up to it running itself, turned on in the middle of the night. I turned it off and went back to bed to find it had turned itself on again but I had to get to work so I just used it. About 5...