Fiberflex 40d jamming
Hello, i printed two 20 hours print with this flexible filaments and no problems.
but after tinkering with the slicer to improove the quality is started jamming almost still right away. any advieces please ? 
RE:
I'm not super professional, but it looks like the filament is melting before it reaches the nozzle. This may mean that you want to reduce the temperature of the nozzle. If you improve the quality, the print speed may slow. Try reducing the temperature of the nozzle. Don't reduce the print bed temperature, as this may affect adhesion. The recommended print temp for that filament is 200-220 degrees Celsius (392-428 degrees Fahrenheit), so try maybe 200 (392) to start with. If this causes the print to fall apart and string, then raise it up, 5 or 10 degrees maybe. If it keeps getting jammed, lower it down by about 5 or 10 degrees.
Hope this helps, sorry about having to wait for a reply.
Edit: "If you improve the quality, the print speed may slow" just gonna elaborate, when you improved the quality, the jamming is likely as the slower print speed (for higher quality) meant the heat transferred up the filament fast enough to melt it and get it stuck in the extruder.