Patches resist resin

I pour the resin (art resin) over canvas paintings of acrylic pour. It comes out hard and clear. But there are patches that resist the resin. I washed the painting with detergent and water and rinsed well. I let it dry for a few days. I made sure there were no fingerprints. And still there were patches where the resin did not adhere. I sanded the entire painting with 80 grit and re-resined. Everything set nicely except there were still areas where the resin resisted. Should I wipe the entire painting with alcohol before pouring? What can you suggest to avoid the bad patches? Thank you.