This worked perfectly for me - thanks!I just went through this today and I came up with a really good solution (at least for my rectangular pool). I ran a piece of strong cord (I used strap material I had around) through the pocket until it was out both ends. Then I tied a loose loop using a bowline knot and worked it around the end so the loop was around the beam. I then tugged hard on the other end until the loop came all the way through (around the beam) . This broke off the stuck vinyl in about 5 minutes a side once I thought of it.
Should work on a round pool but I don't have one so I can't guarantee it.
I second this as the best method. I independently had the same idea so came to post it but hats off to BajanSailing for doing so first. My liner was really stuck so I did a variant. First I passed a 50lb loop of fishing line from the edge of the liner to the first support hole to get the edge of the liner loose. Then, instead of a single rope with a loop, I used one piece of rope looped over the pole with both rope ends coming out the support holes. This helped because in places where it was really stuck I could pull one side of the rope, then the other, to get it unstuck. It works best when pulling along the length of the pole so used rope that reached 2 support holes down from the stuck segment being worked on.This worked perfectly for me - thanks!