UltiJD12

Hi, I have got two Ultimaker s3. Ich have got the Problem, that the material sensor says the material ist empty. After 5h of printing. Material PLA Ich have checked: Material isn't empty. Material ok. Material way to the printcore is good. Printcore is good. If I disable the flow sensor, the feeder block the material and I aboard the print. The feeder is clean and the tension ist ok. I think the speed of 70mm/s and a layer of 0,28mm doesn't work. In think the retract speed is to high, so the feeder block/mill the material. Have you any ideas? Thanks