Context on the printer: bought the kobra s1 combo second hand 1, maybe 2 years ago, don't have the required documents for warranty check.
Noticed a few weeks ago that the no. 2 slot was having difficulties detecting filaments. It would pull a bit through, then seemingly lose it, pull more through, etc until it hit the 4-way split then retract a bit and show no filament on the screen but with a whole roll loaded up as I'd expect. Opened it up on top, found a few loose bits but nothing blocking anything or an obvious cause, put it back together. Now when I try to load no. 2 it'll pull no. 1 through with it regardless of how much is already in the tubing.
Amongst dealing with that I noticed recently that the no. 4 slot will show as having filament when it's empty and will still try to extruder and retract it with the others leading to an "abnormal extrude/retract" error code. Again, when I opened it up I checked that one and couldn't see an obvious cause for it.
Both machines are apparently up to date (in the UK so we're one update behind I think?) and I only print pla at but want to get into petg and abs/asa. I've tried three different styles of filament guides, thinking the alignment was maybe the issue with no. 2, but none of them have solved it.
Added pictures to show what I'm talking about.