Lots of good advice here. I would only mention again...new needle!
Top tension check, re-thread everywhere and replace needle. Always solves that problem for me. Good luck! Let us know!!!

I would guess that you are moving the fabric too fast! I have also had this kind of thing happen. That was the problem. Have you read that if you leave your feed-dogs UP, you have 60% more control while FMQ??? It works! & I don't have this stuff underneath anymore! :-D

Try using a new piece of thread to 'floss' between your tension discs also.

I had this happen to me and my quilt needed to be lowered so that it sits on the bed of my machine...the "gap" caused my loops.

Just last week I was doing small quilt and mind did the same thing! I was moving the fabric faster than the machine was sewing. mostly around curves. go a little slower around the curves and it will be amazing how it helps. also do a search (above) and it will give you more info,

I have a Janome 6600 and I had this problem until my dealer said that she cranked her tension (top) all the way up to 9 or a bit more. You may also be sewing too slow for the speed at which you are moving your quilt around. FMQ is a real art & the skills needed are gotten by practicing and practicing and pract . . . Get the picture? My first attempt went in the trash bin. Even now, I have a practice sandwich that I play with to warm up before working on the "real thing." It's like playing the piano - gotta practice those scales with proper fingering before you can play a sonata.

Good luck and have FUN. Remember to breathe and relax those shoulders. :P

When I'm sewing and suddenly the stitches suddenly look like yours when I know darned well I haven't changed anything, I can generally count on finding some big blobs of lint have built up in the bobbin area or the tension disks.

Check your threading, needle and tension.

Did you magnitize your bobbin area with metal bobbins when it was new?

check to make sure the bobber is threaded properly. that happened to me once