Motorola DP4400 and 4800 series not receiving

I do international disaster response for a living and part of my kit is a mixed set of Motorola radios, DP4400e and DP4801e. Something new has popped up during our current response that I’ve never encountered before and have no fix for.

In short, sometimes a radio (not always the same radio so far as I can tell) will not receive a transmission while another radio in the same room will.

Thinking there was someone else on our freq I tried moving to the next freq but the same problem still occurs.

The problem happens at random and affects random radios. It’s absolutely maddening.

Any thoughts on possible causes or solutions? :confused: