See my post below. I would also add that what your describing sounds like AP turning off below 135 IAS. I think the plane cruises best below FL200. Maybe set that in your EFB preflight.
Also do you switch HV to use external power when you reach cruise altitude? This basically stops battery drain if you remember to turn HV batteries off when in External power mode.
Also make sure you turn LV external power mode on after take off to ensure you don’t lose avionics.