Some advice please.....This is the first time I have had this problem. This is the first time that I have totally pieced both the front and back of a quilt and it is for a gift for my cousin who is due in November. I have been FMQ this in quarters...on the very last quarter this is what I get on the underside (bobbin side). I did not change my settings. Can anyone please tell me what I am doing wrong???? I am now un-quilting this section...Please help, I am desperate.

CHECK TO MAKE SURE THAT YOUR MACHINE COMPLETELY THREADED.

Your presser foot is not down. I can just about guarantee it.

My machine will not sew without the presser foot in the down position, it will beep at me.

either you're moving too fast or you're threaded wrong, may need to tighten up the tension just a bit too, but mostly I'd say too fast

It looks to me like you did not have the tension correct...likely either the bobbin was inserted improperly or the top thread did not feed through the tensioner correctly.

Rethread your machine completely top and bottom and also double check to be sure your needle is not slightly bent, which could also result in a wonky stitch.

If that is the bottom of your quilt, your top thread tension is too loose. The good thing is that the unstitching is easy!

My machine has done this and it's always the threading. I'm not sure how it gets mess up but it does. Redo the thread and the bobbin and then test sew on a scrap.

clean the machine, rethread totally from the spool on, replace the bobbin (after cleaning out all of the lint) and try again. did you rethread or change the bobbin before this started happening? sometimes if the thread is not in the tension disks properly, just laying on them not actually in between them this can happen, that's the reason to start over and rethread, paying attention to each step, give the thread a bit of a tug to make sure it is between the tension disks. if this does not help you need to put together a practice piece and start adjusting your tension...but since the tension was good until now i bet it's either a threading issue or lint build up

I was sewing last night and I hadn't changed my tension, but it was waaaaay off. I had to change it two complete numbers. I don't know if I bumped it or what...
This is what I did:
1. clean out the bobbin area etc...
2. rewind a bobbin.
3. rethread.
4. tweak my tension.