MKS4 with mmu3 printed now will not
I have a MK4S with mmu3. I ordered assembled. Unboxed, attached Rasperry pi with Octoprint (new install), Prusa slicer (clean install).
Proceeded to print test cube 40x40x40 - all OK. Printed 2nd item, all OK. All with 1 filament in 1st MMU3 location.
Loaded 3rd item to print. Single filament no changes. Printer went through preprint warming up etc. Loaded filament via MMU. Started print with the 4inchish line along the bottom of the platter. Then the machine proceeded to print. EXCEPT no filament was extruded, however the machine thought everything was fine and kept going with no filament going through the nozzle.
Canceled the print. Proceeded to extract the filament, using the controls on the printer. Everything fine. Then tested loading the filament to the nozzle and it extruded some from the nozzle. Withdrew the filament. Added filament with different color to 2 location on MMU and proceeded to test loading and unloading. Each time I extruded filament until the new color was coming out. That works fine.
There is not blockage on the filament feeds. The filament is PETG and has been dehumidified.
What am I missing? Why is the filament loading OK. Why is the print head not advancing the filament? I am using all the defaults on Prusa Slicer. But I am missing something?
Help