One adjustment really helped my use of monofilament thread
 

I really, really hate to admit this but after hours and hours of trying to improve the stitches on my invisible machine applique using clear polyester thread (Superior Monopoly), I think I've found the main culprit behind the bobbin threads erratically showing up on the top.

I had done everything I could think of, which helped but did not eliminate the problem- I significantly lowered the top tension, cleaned the bobbin case, threaded and re-threaded the machine numerous times, changed the needle and needle sizes (70 down to 60), etc. These steps improved the stitching a lot, but still quite a few bobbin threads would appear- one small segment good, and another bad just inches from the good spot.

What was my fix and why is it painful to admit? I am working with a new machine to replace a 20 year old mechanical machine (yippee!). I was treating my new machine like my old machine- I just tightened the needle screw with my fingers. After running out of options, I got out my machine screwdriver and tightened the needle screw up (yes, just like the instruction manual said to), and now my stitches have NO bobbin threads!

This may or may not be a complete victory over bobbin threads, but it has helped so much that I wanted to share my experience. Lesson learned!

You're not alone. I realized the same thing when not just the needle was "loose" but the "thingy" that my foot snaps into was always wobbling around.

I'll remember to check the presser foot too! Thanks for the tip!

In many instances it is the simple things that make our machines run smoothly. Thank goodness for the manuals.

When all else fails, read the instructions. So glad you fixed your problem. It's nice knowing many of us are the same in this regard. Thanks for sharing.