I am using 2.12.2, also tried 2.12.0, firmware is 2.2.3. This is a new printer, I’ve only printed Z-Ultrat so far and it worked exactly as expected. The sprocket wheel does not stutter, it turns as expected but the filament feeds erratically using Z-Flex. The stuttering usually experienced when pushing the filament out onto the bed on the very first layer does not seem to be the problem. Sometimes the first layer looks very good then subsequent layers look awful. Other times the first layer looks bad from the start, tiny little strings if there is anything at all. When I remove the filament, it has tooth marks and gouges in it, and the length between the extruder and wheel is all wavey like it was under heavy compression. I wonder if I should change the settings, perhaps higher extruder temp? What settings might affect this?
I did finally get something to print, it printed a raft with many holes and flaws in it but I let it continue until the part was done. It seemed to have less trouble once printing the actual part layers.