I doubt it is because you spray basted it. I just finished a a quilt with fmq that I spray basted and I didn't have any problem with thread breakage. I used King Tut for my thread this time and it worked like a dream.
I also just finished fmq a tree skirt with metallic thread and it broke constantly. I figured it was the the thread since the King Tut worked so beautifully.
Sorry no other advice from me.