I know this is an old thread, but I just wanted to thank
@Ellabella for posting the tip in the first place. It has just saved my sanity!
I've been trying to coverstitch the neckband on a t-shirt, and have ripped it out (very slowly!) three times because of slipped stitches where the band crosses the raglan seams. I've only had my Janome CoverPro 2000cpx a few weeks so I'm a complete novice at it (although I do have a Janome overlocker, so the threading etc is no problem). I was ready to throw it through the window, when I remembered having seen a post on TSP somewhere about raising the feed dogs. Did some research on here last night, and tried making the adjustment before lunch today - success. Yay!
I've also had to lessen off the presser foot pressure a lot as the foot was compressing the jersey far too much as it sewed. I'm sure that's not right but it's an issue I might leave 'til later, after I've stitched the hems, hopefully this afternoon.
Thank you again for saving my project.