hybrid mode

Some - if not all - engine on thresholds - change with the seasonal temp ranges. Making it that much more confusing for the newer owners to understand how the car is programmed.
Don't expect to figure out exactly what the car is doing without changing how the car is driven routinely and just because the car behaves one way for one driver under it's normal conditions doesn't mean it's going to behave the same way for another driver - even under similar conditions.

 

welcome!
you're still under warranty

 

The car is smarter than you. Just drive it. One thing to keep in mind: when the ICE starts unexpectedly, make sure to let it run through its warmup cycle until it shuts down on its own. Never shut down the ICE manually with the Power button during its warmup cycle. If you come to a stop and the ICE is still running, put the car in Park and let the engine complete its warmup before shutting down with the Power button.

 

With the prime it's kinda obvious that shutting down the ICE with the power button when the ICE is still cold, is audibly different, especially in winter, than when the car shuts off the ICE automatically.
Unlike with the Prius, when the ICE runs almost all the time.
The difference is not as noticeable during summer when the ICE is already half way through the warmup cycle as soon as it starts, comparatively speaking anyways.

 

whaf bothers me the most about this is, to get to work I have a downhill (12% grade, about a mile) and I’m EV mode and B mode it will hold me at the speed limit perfectly. There’s a light at the bottom and sometimes as soon as I press the brake, or when I get to about 20mph from 45 it will turn on the engine and in the Dr Prius app I pretty much lose all regen. There has only been one morning that I haven’t lost regen or had the engine turn on. Knowing how and why would be insanely nice as I could get to work 100% not burning any gas

 

That has happened in my pip

 

Bingo. BuscoBob is between some behemoth California mountains. Braking downhill with big battery at bulk charge brings bailout and bleed to engine. To B or not to B is a related matter.
Bet y'all never beheld so many Bs B4...

I haven't heard that B4 either.

 

@False you can learn to manipulate the engine on scenarios to (some degree) by experimenting.

When the temps get closer to freezing in the fall all those experiments go out the window as the behavior changes big time.