Or a signal obstruction.Sounds like an antenna
@Kitzy Can you provide a couple of pix of how the transmitter is mounted on your reg?
The only two things I can think of that the cold might do are (1) lessen the battery voltage and (2) shrink things a bit, like maybe some antenna connection. You've effectively taken the transmitters out of the loop by having a new one plus your old one with similar results.
Some more possible tests:
Switch batteries on the transmitters.
Place the computers where they ae reliably getting the signals and decoding them, and then pack the transmitter in ice and see if the connections drop. Also, not at the same time, pack the coputers in ice and se what happens.