Lost a channel while PiezoFlushing

[steve.in.nm]

Just finishing up flushing my 3880 when I stopped getting any ink flow from the VLM channel. I had clean nozzle checks on the color cartridges before I began flushing with full cartridges of PiezoFlush. Three power cleans, 24 hour sit time, then another 3 power cleans and a second rest period. Clean nozzle checks on all channels with the PiezoFlush cartridges still installed. I then changed over to Piezography Pro inks and used the QTR flush images one by one to clear the various channels. All except VLM have cleared. When running the VLM channel the PiezoFlush cleaned out but no Warm Medium ink is running. A nozzle check shows everything is fine except this channel, which is empty on the nozzle check. A copy of the last QTR flush run is attached showing where everything stopped flowing towards the bottom of the page.

I checked the cartridge and it looks ok, including the diaphragm on the back where the ink flows into the printer. The 3880 recognizes all the ink cartridges. I did have a self-inflicted problem with the previous cartridge I used for this channel where I somehow damaged the exit diaphragm while priming. I noticed it was leaking when I installed it, but there is no visible damage.

What should I look for at this point? I assume the damper is ok since the PiezoFlush went through with no problem.