Our Gateway uses a NRF52 and the sensors a NRF51.
Gateway is outside the freezer at + 20C and the sensor is inside the freezer at -30C.
What we see is the pairing becomes more and more difficult is the temperature difference increases.
Of course we use batteries that still provide enough power at -30C or -40C for the sensor to work.
The beacon signal of the sensor is received by the Gateway but pairing becomes increasingly difficult.
Can there be a timing issue? The sensor listens after every beacon signal and wait for a pairing request.