Could also be hydrostatic pressure - this happens to a lot of people in spring when groundwater levels are higher than normal.
If you have a leak, then your water level should drop, if it hasn't, then it's likely hydrostatic pressure. Has it rained lately?
Most IG pools have a sump pit with either a wellhead to stuff a hose down to pump out or allready have an actual submerged pump in the pit with a hose or piping emtying somewhere in the yard.
Probably, your liner is floating up and away from the sides because of all the water collecting under it.