It's my understanding you have a probe for measuring underwater temps. I would check the calibration on the probe/gauge setup and assuming it's safe to go out on the ice, go and take some measurements.
You can use an ice bath with some ice cubes and a little water in a bowl to get a single point verification @ 32f.
Plot a profile of temp vs depth with and without aeration.
I would think the pond would start to stratify after a week or two after removing the source if aeration were actually causing the pond to mix.
You posted a few weeks ago that you had a 35F bottom temp. Assuming that was an accurate measurement, something caused that. It should be 39F. Perhaps you were right up against a loop or perhaps they had already floated.
I don't think the single digit temps could have anything to do with that assuming you had ice coverage insulating the pond and protecting it from wind.
