Welcome to the Quilting Board!
It looks like your presser foot might not be lowered when you're stitching. It can cause this kind of problem, and so easy to forget.
When I get that it is normally because my top thread has pulled out of one of the guides or my bobbin thread (for some reason) has come out of the guide there. This sometimes happens when my thread breaks, so I do make sure each time that my thread is still through all of the quides.
I am going to be watching this "thread" hints and possible reasons.
I choose to give my life away for things that last forever
Mine does that when I am in a hurry and don't have my machine threaded correctly.
Check threading,bobbin, and be sure pressure foot down.
During a long arm class, they said if the problems were on the bottom is usually was a problem with the top and threading or such. It is the reverse of what I thought.
I have a Gammill and sometimes find this mess in the last twelve or so inches I've quilted. The problem? My thread comes out of the tension easily but will carry on like it's fine. So you have to be vigilant...and I also laid some mirrors on my table to watch the back more closely.
If you feel like you're special...it's 'cause you are!
Wish I could help