@Falc.be I had exactly the same issue with some grey XT I've got. My prints were functional, but not pretty. I didn't try creating additional extrustion at the start. In fact, I just ended up moving to some other jobs, but I'll be interested to see if you can find out what's causing that for you.
switched colors on the extruders. I had no idea that only the color of the filament can make such a difference.
Each pigment is a different addition to the material that will have an effect on material properties. I've not experimented a lot with XT, just that grey stuff, which seemed not to print too well with the settings I had. I'm glad to hear other colours might give different/better results.
After trial and (mostly) errror I think I finally nailed my quality problem I looked at the toolchange script more closely and I saw that during purging, it retracts with a feedrate of 6000, thats a retraction speed of 100mm/s ! XT needs a slower feedrate and a bit more force than PLA to feed and retract from the nozzle. if it goes to fast the filament will grind and it will be even harder to push trough, causing underextrusion and eventually clogging as I found out later. This is my script so far (for use with scaffold) ;BigBox Oozeless Tool Change Script Begin ;retract to move G92 E0 G1 E-1.5 F100 G92 E0 ;dock {IF OLDTOOL=1}G1 X105 Y200 F3000 {IF OLDTOOL=1}G1 X105 Y240 F3000 {IF OLDTOOL=0}G1 X70 Y200 F3000 {IF OLDTOOL=0}G1 X70 Y240 F3000 ;purge {IF OLDTOOL=1}G92 E0 {IF OLDTOOL=1}G1 E25 F400 {IF OLDTOOL=1}G1 E-14 F2000 {IF OLDTOOL=1}G92 E0 {IF OLDTOOL=0}G92 E0 {IF OLDTOOL=0}G1 E25 F400 {IF OLDTOOL=0}G1 E-14 2000 {IF OLDTOOL=0}G92 E0 ;extruder steps per mm {IF NEWTOOL=0}M92 E302.8 ;adjust steps per mm for your filament in extruder 0 (L) {IF NEWTOOL=1}M92 E288.15 ;adjust steps per mm for your filament in extruder 1 (R) ;prime new extruder {IF NEWTOOL=0}T0 {IF NEWTOOL=0}G92 E0 {IF NEWTOOL=0}G1 E25 F200 {IF NEWTOOL=0}G1 E-1.5 F200 {IF NEWTOOL=0}G92 E0 {IF NEWTOOL=1}T1 {IF NEWTOOL=1}G92 E0 {IF NEWTOOL=1}G1 E60 F200 {IF NEWTOOL=1}G1 E-1.5 F200 {IF NEWTOOL=1}G92 E0 ;undock {IF NEWTOOL=1}G1 X115 Y240 F3000 {IF NEWTOOL=1}G1 X115 Y200 F3000 {IF NEWTOOL=0}G1 X80 Y240 F3000 {IF NEWTOOL=0}G1 X80 Y200 F3000 ;BigBox Oozeless Tool Change Script End
I had trouble with Grey XT even with a single color print. Probably the result of retraction, and yeh, could will be related to this need to restract slower. I think the same is true for flexible filament.