Happened to my last pool and we bought new trim lock that foced the liner back into the channel sold at local pool store if I recall we had to heat the liner area to pull it enough back to get the extra length to get it into the channel. Then it pulled back out and eventually the liner tore in that corner and had to be replaced. Seemed like there was pulling to the area maybe caused by a small leak in the liner somewhere was what the 1 guy had said.