I have a Bernina too. Not sure if your foot is worn out, or if there is possibly an adjustment that could be made to the foot? Are you getting this happening when going over seams? Or just flat quilting? Sometimes I have had it do that when stitching over the seams, but then fine when doing the rest of the quilting.
I don't use mine a lot, mostly quilt free motion, so I don't think my foot is worn out.
Hopefully the Bernina dealer will be able to help!