Update is that I am still losing water. It is not that fast but certainly a lot. Pool will be empty within a day or so. I can only believe it is the hydrostatic valve. It started draining after I started the pump, when the skimmer sucked air a few times.

I think my only hope is that I can get to it when the water is low enough. It is way too cold to dive into and fix now. I am open to suggestions.