I had a lot of problems with the Extruder Drive. I had the feeling it did not press into the PLA hard enough to get enough 'grip' and a lot of prints were lost.
I fixed it by sanding out the U shaped part were the spring pushes into. I sanded the bottom of the U to give it a bit more range. I also sanded the parts of the black plastic part that pushes into the wooden part of the extruder part. This way the little wheel that pushes into the PLA has way more drive so it gives you way more range in tensioning the spring. If I can press in the wheel with a force of 15kg I get no failed prints anymore. Too hard and it will jam, too light and it won't push any PLA through.
Hope that helped!