Initially I had problems printing flexible TPU filament on my CR-10S printer. It liked to ravel between extruder wheel and PTFE/Capricorn tube, especially after frequent retracts.
The problem with soft filaments is that frequent back and force pulling will squeeze the filament making it more flat and wider, so that eventially it can not be pushed back into the PTFE tube and forms a clew.
There are several solutions to mitigate that problem
1. control/reduce pressure of extruder wheel (this thing) 2. cool the step motor of the extruder too avoid making filament even softer (I used a simple little USB fan for that) 3. tune rectract parameters, push back filament slower
Actually after controlling extruter tension (avoid squeezing) and keep it cool I have no more issues with flexible/TPU filament.
The tension control reuires a simple M5x10mm (knurled) screw + nut