I really don't know how to explain this so I've posted a photo.pool liner.jpg
The top of the liner is supposed to stay behind the track above it. Here you can see an approx. 4 inch section that has slipped out of its track.
If I press it, it will go near to where it should be but not stay. It's really difficult to press like there is extra wall foam behind it. But I don't really know.
This is the only spot I've seen like this.
How worried should I be? Can I fill the split with silicone (it's less than 1/8") but I know silicone won't keep it from spreading if that's what's going on. Or should I call the installer? The liner was replaced 4 years ago when we bought the house.