Hope you get this figured out!
Pictures are a big help. The Help section has some good guides, posting pictures here isn't as intuitive as maybe some of us would like.
https://www.quiltingboard.com/qb-help-center-f27/
So do you get a big nest of bad stitches on the bottom, or is just one or two missing?
Any details on the type of fabric -- is this all the time or just the current project? Sometimes people can have issues with tight weaves like batiks for example.
I believe in replacing needles often, even if you've just replaced it sometimes you get one with a burr or manufacturing defect. If you hear a "pooka pooka" sound while you are stitching, it means your needle is beyond dull and is punching holes in your fabric instead of cleverly slipping between threads.