The stitches on the underside are looping I’ve retreaded both the needle and bobbin and neither makes a difference

SOURCE: Janome Memory Craft 9500 Troubleshooting

The solution that I found last night was the thread tension. I have never touched the dial, only had it set on 'auto." When I started playing with it, I realized the top thread should be really easy to pull through the machine and it wasn't. I started turning the dial (to 3 or 4) and the thread slid through the machine perfectly. No more birds nest! I really thought it was bobbin initially because of the horrible sound it was making.

SOURCE: Thread loosens underneath intermittently. Stitches not consistent.

take it to a serviceman.

SOURCE: Bobbin continues to pose problem - knotting thread underside of fabric,

In 99% of all problems with "bird's nesting" or "knotting" it is an issue of the thread coming out of the take up lever (at threading guide #3) (from the spool; through the first thread guide at #1 down to #2 and up to # 3) when the thread comes out of the take up lever, the machine can not regulate the thread and it floods the machien with thread and wraps itself around the bobbin case. OR! Your tension is too loose. Raise it. Your machine should preform perfect at tension #4 unless you are using speciality threads or fabrics.

ALWAYS be in the habit of threading your machine with presser foot up so that while threading between paths 1 and 2 you are certain to have the thread pass throught the tension disks.

This will happen on a $50.00 machine or a $5,000 machine. The thread needs to be regulated.

USE GOOD THREAD!

Thanks,

Bonnie

SOURCE: tension

Several things to try, I have this set up and after six months I'm still trying to get some issues resolved.  First make sure the machine is treaded correctly, the Juki doesn't thread like most machines, make sure you have the bobbin going the correct way.  After the machine then it has to be in the frame which means that the fabric is most likely to tight, this is a common problem, if you are bending the bars then it is too tight.  Also, look at how the quilt is in relationship to the frame, is it level?  As you quilt and roll, you will need to adjust the frame up, the quilted part should not drag on the machine and the to be quilted part should not be below the machine.  It is a critical that the frame and the machine be even with each other, if not the machine will try to pull and won't sew correctly.  Also, another tip, after each quilt change your needle, the reason is that free motion is technically bending the needle.  Hope all this helps.  

SOURCE: Singer CG 550 Top thread keeps wraping around the bobbin and jam

Have you checked the top thread is correctly placed in the spring of the bobbin case?