I don't know much about invisible thread but is it possible that it is not coming off the spool correctly? May you should try turning it around and see if that helps. Colleen

I did try that, to no avail, but thanks for responding.

In addition to what's already mentioned:

Try a heavier weight of monofilament? Maybe the stuff you have is too thin, and is stretching/getting tighter as you sew.

Using the same thread in bobbin & spool?

Larger needle, to make a bigger hole? If your layers are thick, you might need a 14 or even a jeans needle. Switch from a sharp to a ballpoint, or vice-versa.

Try smaller or longer stitches?

If straight-stitching, try your straight-stitch plate, if you have one.

Stop sewing with needle in fabirc, lift presser foot and then resume sewing every few inches?

Flip it over so whatever fabric is on top is on the bottom instead. Perhaps one of your fabrics isn't feeding at the same rate as the other. You could also try a teflon or walking/roller foot for same reason.

A couple times my computerized Viking machine has "lost" it's auto tension, causing problems. I have to unthread it, turn it off, turn it back on and rethread it.

I believe my machine just does not handle the monofilament well. The Bernina shop closest to me just closed permanently and no place nearby carries any other size monofilament. I will try your suggestions. Thanks for the ideas.