Skipped stitches
Hoping someone has some advice on skipped stitches that I haven't thought of or seen elsewhere because I feel like I've tried everything at this point!
I'm quilting a throw-sized quilt with a walking foot on my Brother PQ1500SL. I've done lots of piecing with it and quilted a table runner but this is the first time I've used it for a proper quilt. When I quilt through thicker areas (triangle points) my machine skips several stitches before/after the seam. Seams within the rows are pressed to the side and the seams connecting the rows are pressed open and as flat as I could get them with a tailor's clapper. I've attached an image to illustrate. I got a rare skipped stitch on the table runner but nothing like this.
So far I've tried making sure there is no drag around the quilt (set up on a big L-table, nowhere the quilt can snag), increasing the stitch length (3.0), going suuuper slow through those areas, re-threading and cleaning out the machine, checking the walking foot is properly installed, fresh needles (quilting, microtex and jeans), a larger needle size (up to 16), and lessening up on the presser foot pressure (I'm in the pink zone on the machine's guide).
I'm kinda out of ideas and so tired of picking out my quilting! My next call is to take it in to see if they can find anything mechanically wrong with it. But before I do...is there anything I haven't thought of??? Thanks so much for any and all advice!