I copied the same curves to both machines. Also did an UNINSTALL and reinstall on the El Cap machine.
These Eboni 4K curves have worked beautifully on the Yosemite machine for months. We linearized them with Richard's Gray Curve spreadsheet, they were nearly flawless.
Lightroom and Print Tool both work perfectly on the Yosemite Mac. With the exact same curves, neither of them work on the El Cap Mac. I have the correct ink set. Perfect nozzle check.
Thanks for your help,
Parker