I think there're 2 issues adding up to your frustration. 1. Your rope is new. My personal rope is Samson /BWR. When I 1st got it I couldn't footlock with it to save my life. It was very slick. It took me about 20 climbs to get it "furred up" a bit. The Safety blue I use for my climbing academy was the same, but seemed to break in quicker. I've only used PI three times, and it seemed pretty slick too. So give your rope a few dozen climbs to break in a bit. 2. Your footlock technique, you simply need to get more practice with it. Keep at it and anylise what you're doing a n d b e p a ti e n t. I'm guessing that you're a persistent kinda guy. You will get this worked out. I work with pros who can't footlock all that well. So don't sweat it too much. You'll be fine.
Ron