Help - individual channel not sending signal to the dimmers

On my Express 24/48 I have one channel (#4, if that matters) that shows activity on the monitor, but is not sending a signal to the dimmer rack. It's the same on both presets. The sliders are being recognized (because the monitor shows it) but any dimmer patched to that slider does not come on.

I have a high school play opening next week, and I kind of need this to work. Worst case scenario is I repatch those dimmers into a different unused circuit, but when I have students running the show I like to keep things organized.

Has anyone seen this, or heard of this, or know what else I might try?

TIA

Ed

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