If you used starch to iron your backing it may also interfere. I use Dritz and never had a problem with it and some of it has sat on my shelf for over a year and still works.
Are you spraying the fabric or batting? Spray the fabric not the batting. Batting is very hollow and the spray goes into the hollows and so has less sticky area to grip. Fabric is flat and has more area to hold the spray where it needs to be.
Try this on a scrap and let us know how it worked.
peace