Adding a third (recieve only) SiK radio causes trouble

Having two SiK (HM-TRP 433) radios work well, I am trying to add a third for receive-only telemetry:
The third’s radio duty cycle is set to 0%
It is not connected to anything that transmits data (no GCS that send heartbeat or such)
The presence of the third radio, causes problems to the others.
Does anyone know how this can be accomplished?
Maybe @tridge has some way I can change the software to achieve this?