I agree that cold weather effects are worth serious consideration.
Bike performance can degrade by 15-25% depending on how cold the weather is, particularly if riding in cold damp air or precipitation that lands on the battery case.
One mechanism for this performance reduction is that the chemistry winds up with increased resistance to current flow in cells at lower temperatures. The other is that colder air is denser (and wet air is much denser) which increases drag and the demand on the motor will be higher.
These effects usually start at about 45F (7C) and get more pronounced as it gets colder.
The effect of the SoC rising as you stand still is a little odd but can happen because the coldest cells probably absorb heat from their warmer neighbors (the cells not at the edge of the battery case).
First, what ambient temperature are you riding in? If you check battery temperature on the Zero app, does it seem to dip as you ride (this is less certain because there are multiple sensors but can happen)?
My typical suggestion for this is to try covering the battery securely with an insulating sheet, just enough to keep the cold air from directly contacting the battery case. If you put a sheet of hard plastic (â…›" thick neoprene or polycarbonate) behind the front cover, you might see a good amount of your range/performance return.
Now, there may be another explanation that is about how SoC is computed (it's not a direct measurement; the firmware has algorithms to decide what to show you) where maybe the cold weather is throwing it for a loop. But I can only guess that if it's true, then SoC will probably act more normal the more you ride in cold weather.
