Visible threads are the downside of a longarm quilters life. No matter how carefully the maker presses and trims their quilt and how carefully we mount the top, backing and batting on our machines, there are always some threads that end up showing in places they shouldn’t. I inherited my grandmas knitting and crochet tools, and in there is a really fine crochet hook, fine enough to be inserted carefully between the fabric threads and able to pull out the dreaded visible stray dark thread. When the “bad” threads have been removed, you can stroke the thread fibres closed over the hole that you pulled them through and no-one would notice any unusual marks or ladders in the fabric. I hope this helps as even when there is dense stitching, those threads can still be removed leaving no marks, just beautiful quilting results.