Epson 7900 DTF Missing all Nozzles But Print Head not Clogged

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Hey Guys. I have 2 Epson 7900 DTF Printers that have been working great for over 1 year now. I decided to take a vacation and Installed cleaning cartridges in them filled with Piezo Flush Cleaning Solution. Purged all the inks from the Ink Tubes and print head and even ran a nozzle check, and all printed perfect with the Red Piezo Flush on both printers. Came back from vacation and ran a print head clean and nozzle check and noticed 2 nozzles not printing at all. So I ran another nozzle check and ended up missing 2 more nozzles. Same happened with 2nd printer. Check the printers back the next day and all nozzles stop printing. I removed both print heads and used a syringe to check each nozzle and all were completely clear, but for some reason the nozzles just stop printing. Have anyone here had this issue? I’m thinking the Piezo Flush ruined my Print heads on both printers, same issue. Would really Appreciate your Reply.

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This post reflects very much my experience.
I have two channels with virtually zero output which seems to indicate a blocked ink supply rather than a head issue unless the access port on the print head is blocked. I can squirt fluid into each head channel which seems to indicate no blockage there. Is there a failure mode that causes all the channel head print outlets from failing together? I would expect a driver board failure to take out only one print outlet if it failed or a total board failure taking out all channels.
I have checked the cartridge by pressurizing the cartridge out of the machine and pressing the valve with a n open paper clip. All ok. I have taken out the damper unit and can detect no difference between the failed channels (orange and Black) and the others that give a perfect print head check pattern. Interestingly I can pass liquid freely from the print head side of each damper channel but not the other way round. Does anyone know why this is? So apart from the tubes what"s left?
I am reluctant to buy expensive head and damper replacements without a clear indication of the failure.
Has anyone any other insights particularly on the possible failure modes of the head?
regards