I love Invisafil for Fmq when I want to do micro quilting for texture. I went back and read the posts from 2015 that you mentioned and was surprised that folks were having problems with it. I use it in both the top and bobbin thread on my PQ1500s and it does great for me. Never had a problem with breakage. Because it is so fine and can be slippery I use all three holes in the pre-tension bar on the Pq1500s.
Rob