Hi together,
I have sometimes problems with filament retract. The ams cant pull the filament. When i now touch the ptfe tube of the buffer ( wiggle an bit, or disconnect it at the printer side ) it makes an klick and it can retract. Same with the hub instead the buffer. Has anybody an solution ?
Change the orientation/routing of the tube. The problem is that the filament is binding. Someplace, the tube is being bent/curved at too sharp an angle. If necessary, use some duct tape to force the tube to stay in a “straighter” path.
This cant be the issue. I have no sharp turn on the complete route. Only the buffer or hub stays in some cases “locked” and an little touch of the tube between buffer and printer make it retract able, you can feel it the buffer is then doing something
You can hand feed filament by hand and see if you can find the binding spot.
I know some people have had to cut the tubes at the printer coupler causing filament to bind and also inspect the coupler internals.
Some people have also need to use a filament Tube Guide with the AMS.
The coupler in the top of the extruder has also been known to bind filament if using cf filaments but I don’t think this is your problem. By the way you can move the tube on the rear of the printer.
Keep us updated 
Hm… yes… this maybe an solution this i wil try… open and close the coupler during retraction process work too… i going to install there an good quality coupler ( i have some from festp for pneumatic fittings ) and look what it does then
An other coupler did the trick 
i posted it in an new topic for others have this problem too