Sorry, trying to follow here. Three locations: front door, kitchen and living room. 4 detectors: original front door, new front door, kitchen and living room?
Original front door went off in situ and in the living room while holding it?
New front door went off at front door. Swapped NFD with living room - NFD went off in living room.
Moved NFD to kitchen and it went off in there too?
Where are the K and LV detectors now? Have any of those gone off anywhere in the house? Are THEY functional? (Sorry if you already said, I’m trying to piece the bits together and mighta missed that)
Have you ruled out other types of fumes? Eg fresh paint, perfume, scented oil diffusers etc.