Ok Cool, so when you load the filament how far towards the splicer does it travel? you should see it go just past the cut off blade. I would video mine but i’m in the middle of a print right now. but I have attached a still picture that we can use.
when you put your filament in the feed wheels at A should grab it and move it thru tube B to cut-off area C.
if it stops at A before B then there may be an obstruction in area B or the filament sensor has some debris in front of it causing it to think that there is something in the tube already. same applies to area C.
This upgrade kit install video is one of the best I have seen for helping you get familiar with your palette. you could try and swap a sensor from tube 1 to tube 4 if all else fails.
https://www.youtube.com/watch?v=5syFY4vy...
also take a peek at this video to see if it applies to your problem
https://www.youtube.com/watch?v=JUrblIVP...