(I have not read all the comments.) I have a singer 403 and a vintage white/new home. One time, my 403 was out of commission and I used the other machine (can't check what it actually is-it's at DD's on permanent loan). I was sewing nylon straps on fabric grocery bags. The other machine simply would not sew without nesting thread underneath. The singer has no problem with straps, velcro, anything. It just powers through. Your machine may just not be strong enough.

Great tips everyone! Hate sticky velcro!! Lol

I never try to sew the sticky velcro and when I sew the other I use the zig zag and have used the straight stitch and it worked for me!