I can print multicolored on extruder 1 to 3 without any blockages no matter how many tool changes are done. But when I add the 4th extruder the filament will get stuck eventually in the steel tube of the Y-Splitter after ~200 layers of printing (I can print flat objects with 4 colors without the filament getting stuck). Then I have to unscrew the QSM-M5 fitting of the multiplexer, cut the filament above the steel stube and push it out the other way.
The fact that it only happens on the 4th extruder and only after a while lets me believe that it is not a printer/slicer setting but some hardware issue, like not perfectly aligned steel tube or the steel tube being just a bit too narrow or the spring tension is not right. I tried to fiddle around with all that but without success. Does anyone have any other suggestions I might try?