So the question is, am I missing something that lead to the heater legitimately freezing or have I encountered a bug due to relying on stored power during the night hours?
I loaded an earlier save and paid a little more attention (and added some extra redundancies) I can (not so) happily say it was a me issue. What I had done is increased the heaters service area to cover a nearby drone hub but I completely forgot to recalculate the power usage. I went from having lots of reserves to exceeding the day time production so I ran out of power within one Sol. I most likely ignored the power shortage warning because I was building it at night so I expected to see it pop-up and assumed it was the usual nighttime/solar panel reason. Oops.