Thank you to all you wonderful people who've offered suggestions. I am trying them out as fast as I can. I built up more area around the extension table to help reduce any pulling, changed the stitch length to 2.5mm, pulled my quilt up the best I can (am hoping to get some elastic & hang from chandelier tomorrow) & all that has resulted in a slight improvement, but has not resolved the issue.
Feline, I suspect you may be right about the extension table being part of the problem. It's such a strange design -- not flat & not particularly smooth either. I bought an Ikea INGO table that I found an Ikea Hack for turning into a recessed sewing cabinet. I haven't started working on it yet, but maybe that needs to move up my list of priorities.
Annette, thank you especially for your feedback. Yes, I think that almost certainly is the problem. The photo I posted doesn't show it, but the irregular stitches show up regardless of where it falls on the seam. I think that the crooked seams are the result of the irregular stitches more than the other way around. I know it's a new machine for me, but I've been sewing for over 25 years. I haven't sewn such crooked seams in over a decade.
I also can't help but wonder whether that sole with the ditch guide on it is creating some of the problems. I'm going to try a regular sole on it & see if that helps. Unfortunately, I've been less than impressed with my Bernina dealer. Really wish I would've read the Yelp reviews before buying from them. On top of that, the 350 seems to be a dust bunny magnet. I have to stop every 90-125" of quilting, break thread & clean out my bobbin case. I'm using Aurifil thread & never ever had this issue with my old Singer machine. It's just ridiculous, but you can hear the machine sound change from the lint build up. I oiled my Singer machine once a week. Bernina says to oil their machines once a day & sometimes I end up having to double up on that because you hear that dreadful screeching sound. So far I am really unimpressed with this expensive new machine. Wondering if I would've been better off buying an old Featherweight.
