When working with MMU2 the most important thing is that the melted filament tip need to have a proper shape and diameter so it doesn't jam the extruder or the pfte tube. I'm working most of time with PET-G so i had a lot of stringing problems when unloading the filament. At first i've tested few g-code sequences that moves the filament from hot to cold zone trying to shape the tip but that was not enough. At second attempt i've lowered the hotend temperature to 220°C right before unload sequence and back to normal temp right before filament loaded... and now it is working good.
The last thing i need to do right now is the wipe towers postprocessor script for slic3rPE