This article may be helpful. I would test it on a stand in the garage/home and see if the problem persists in warmer temps. It looks like DOT is better than mineral oil in extreme cold, IE much colder than what you are describing...
I have a version 2.0 kranked kit I bought used. It is about 6 years old. I have retrofitted it to an XC bike for the time being. It is all throttle controlled, pedal assist at my discretion. I have a 52v battery I keep in a backpack while riding. It has a Kelly controller which appears most...