Opened Pool to find a Lose Liner. I wonder what caused that? Any ideas?

[Bevly]

We suspect we took the water level too low causing the liner to contract and pop out in places. Not sure if that is the case or not cause it happened mainly just in the deep end.
Our first year we let an experienced pro close the pool and they kept the water level just a few inches below the skimmer basket and we had no issues at opening.
Just curious what other's may suspect happened here?
If not the lower water level, might age alone have some effect on the liner and liner lock?
Thanks. Just curious.

 

[cowboycasey]

liner's tend to come out over winter, not sure why, hot water and a hot day will allow it to be stretched back in and liner lock put back in..

 

[basod]

I've had a few spots pop out over winter.
My guess is there is some moisture/debris in the track that freezes and pushes it out.
Depending how far it has dropped it is easier to get it back in with the water level low.
I use a hair dryer, good set of knee pads and prepare to burn the front of your knuckles off