Running a FLIR E8-XT in my Victorian terrace for the past eight months and I can confirm that repeating cold spots are far more likely to be boring physics than your dead gran popping in for a chat.
That said - far more likely isn't definitely, and that distinction matters.
Before you get excited, rule out the mundane:
Thermal bridging through external walls (corners are notorious for this), Cold air pooling from a gap in the skirting or floorboards, HVAC returns creating consistent airflow patterns, Simple radiator shadows - corners are often the last place heat reaches
Log the temperature differential over at least two weeks with a data-logging thermometer (Govee or Inkbird units are cheap and reliable). If it tracks perfectly with outdoor temperature drops, you've got a draught, not a ghost.
However - if the cold spot appears at the same time each night regardless of ambient temperature, that's where it gets genuinely interesting. I had exactly that situation in my back bedroom. Turned out to be a blocked Victorian fireplace creating a weird convection loop. Anticlimactic? Absolutely. But it taught me that unexplained doesn't mean unexplainable.
What's the construction of the house and what readings are you actually getting? Drop some numbers and I'll tell you whether it's worth dragging your EMF gear out or calling a plasterer instead.
