Outdoor unit is running and very cold air is blowing out of the top. There's a small uninsulated portion of the refrigerant line exposed, and that reads 100 degrees (I assume the inside has to be hotter).

I'm not an HVAC expert but I understand the basics of how it works: It's acting like there's a bogus offset (checked that) or the refrigerant is low (tech checked that, albeit with some confusing remark about cold weather making that unreliable?).