I have new thoughts since last time based upon what went down in my build. I did a slab under the pavers, and when I tested the slab for drainage, a big part of it went towards the pool and right under the liner track. The result was a large bulge in the wall which took a while to drain.
If you zoom in, you'll see some decent gaps under the track. That's where your water is getting in IMO.
The liner bead in the liner track, even if it's a little loose makes a very difficult path for water to travel. Water running off the top of the patio wouldn't defy gravity to go into the wall, around and under the liner bead, then up and over the bottom edge of the liner track to get behind the liner. It's pooling in a cavity under the patio and going right under the track and liner.
Get in there or hang over the side to inspect the edge where the liner track meets the patio/coping. If there is a gap/crack/cavity anywhere along that wall, that's your source of how the water is getting in. Instead of using liner lock they pounded the top of my liner track every 6 inches, each leaving a gap, which I caulked.
If your inside coping edge is sealed tight, then look to the patio seems. One of them, possibly not the obvious choice, is funneling water under the liner track.
