New ingroud walls slightly bowed

[Stacy]

We had a new ingroud pool installed last fall. We filled the pool 2/3 and it was covered for winter. We have never used the pool and noticed as we were getting is started today the walls on the one side are slightly bowed. The pool place we purchased the pool from thinks it is from the ground shifting over the winter. We are filling the pool up tonight.. hopes that it bows back out. Anyone know if this is a ground issue or an install issue? We havent ppoured the pool deck yet so pulling the sand away may help to relieve the pressure? Any thoughts would bre greatly appreciated before the concrete is poured. Thanks