ColorSource Spot & Cyc fixtures periodically stop responding to DMX control

Hi all, 

In the studio space at one of our schools, they have a mix of ColorSource Cycs, Spots, PARs, and Source Four LED Studio HDs. For the most part they've all been working great, but once a month or every other month one group of fixtures (a run with 2 CS Spots and 4 CS Cycs on a CS Relay) stop responding to DMX completely. Sometimes when this happens, one or two of them will also reset to address 1. The only way to restore control is to power cycle the fixtures, after which they'll work totally normal again for at least a month. It seems to happen with or without RDM enabled.

Their system is controlled by Nomad with a Gadget II, through a DMX/RDM splitter, to 4 CS Relays. None of the runs from the other CS Relays are ever affected, and the problem still occurred after switching to a spare CS Relay.

Any ideas on why this might be happening?