Have you googled and looked through all the youtube videos for your machine?
https://www.google.ca/search?q=learn....0.q0s-i5IDu6Y
I have the 870 so different than yours, but I know if I have chosen just one different setting things don't work quite like they are supposed to.
Does your manual tell you what settings to be on? Mine has a few warning settings, like not letting you do a zig zag stitch when you have set it for the straight stitch plate (just a thought)