A bad cable is the obvious thought when something that was working OK stops. The other obvious question is what changed?
I will ASSume using the TRS insert cable which is single ended and unbalanced is what changed. The TRS insert is effectively two, two-circuit paths, one coming and one going using a common ground and common audio low reference. There can be issues when there are ground potential differences between the ground at the console and ground for the outboard gear.
Are they plugged into the same mains outlet? Is there other gear in the rack with the outboard gear (like a power amp) that could introduce noise into the rack rail ground?
If properly designed the insert point should use differential circuitry inside the console and be clean WRT the sleeve ground at that console insert jack, but if there is noise current flowing in the insert cable ground between console and outboard chassis, that can corrupt the audio signal integrity.
One strategy is to rewire the insert cable to use a differential (xlr) input at the outboard gear input, where the ground from the console insert jack connects to the outboard gear, audio low reference (pin 3) input, and tip to audio hot or pin 2.
But try the easy things first, like where the power cords are plugged in. The TRS insert system works well, most of the time.
JR