Thanks for the nice summary with detailed information.
I had exactly the two same errors like you and corrected a view things.
- If you use Orca-slicers K2+ printer setup you need to change some flags in the multimaterial settings then otherwise it creates purges into the brim tower which generate then clogs in the extruder and even when retracting filaments!
- I had to change extruder shell because the tube holder was broken
I made also some mods for the tubing (K2+CFS modifications: The extruder and CFS tubes & connections) and to CFS but since then ( a month now) I had no error whatsoever!