You probably need to re-time your machine. the owners manual should explain how. Or look on youtube. they are so helpful.
I have a 10 year old Gammill.Bought new. I had it serviced early this spring.And every now and then I get skipped stitches,also about the same place.What I noticed is I was extending my arms very far out.Also a little sideways.Is it possible I was moving it crooked?I don't know.But when I quilt closer to my belly bar and straight on,I don't get those skipped stitches. Just a few thoughts.