When loading and unloading filament, there is no cancellation-button. Also i have not found any way to move the filament just a little.
When unloading filament, i have had the filament stop due to the end of the filament being a small blob. i have then removed the ptfe tube from the extruder driver side, but the blob is to far in for me to reach with my cutters, so i need to feed the filament out a little. Being able to do this with either loading and then cancelling, or by manually feeding a little bit would be handy.
I am not sure if this is something we could potentially change ourself, i have not dove into the marlin side of the printer, but if someone would add that functionality, that would be neat.
I just use the release lever on the extruder to load or unload filament. I only have one of two heads working (solenoid failure), but doing this methods I have done multicolour prints on this printer. Make sure hot end up to temp.
Maybe your PTFE tube is not pushed all the way into the hot end? If gap, this could be cause of blob.
I did some investigation on this. From what i could feel the PTFE-tube was pushed all the way in, there was a distinct stop. However i found out that the PTFE-tube was cut at a slight angle, this could possibly have led to some leakage outside the tube which caused the small blob to form. I cut the PTFE tube straight with a razor and the unload after that worked great.