The only time I have ever seen EOT data being re-transmitted was in some cases of mountainous terrain with tunnels/valleys, etc where the head end might lose communication with the rear end due to these tunnels, etc. However, in those cases, I never heard them transmit if there was no train around and it was relatively low power, just enough to bridge the connection (same applies to DPU transmissions). Is there a chance you are getting "digital" interference from some nearby towers or something not railroad related?
The head end frequency from the locomotive (452.9375 MHz) does transmit further than the EOT does (457.9375 MHz) but I would still expect a train to be reasonably close to pick up either of these. I assume Canadian railroads use these same frequency pairs but if not, they might do something different.
I can't imagine a reason any railroad would use a high power, long distance configuration to repeat this data. While each EOT/HOT has a fixed address, there would be tons of data collisions if this were to be done (and there probably already are in large yards).
Hope this helps and maybe some other users can chime in with their experiences!
It’s probably Ducting, I just wasn’t sure the UHF would be effected by that.
An interesting sidebar to what Alabamarailfan was saying about tunnels and valleys is a number of years ago while in the Gallitzen PA area I heard the dispatcher relaying brake pipe pressure to a train going through the eastbound tunnel. He must have had the ability to decode the EOT signal and broadcast it over the VHF.