Pool floor sink holes in new pool

[Gordo]

After new pool install I noticed a 5 or 6 inch diameter area on the pool floor where the liner sunk in or the sand fell away. In this hole the liner does not feel like its supported by sand.. We had a great deal of rain right after the install when there was still only about a foot of water in the pool. I dont know if this is the cause.

Over the past few days I noticed that the same thing is happening along every side support of the pool (oval) the exact same size sink hole has formed on the pool floor under the liner at each upright support along the side of the pool.

The store said not to worry about it and that they would like to come back at the end of the season have me drain the pool, pull back the liner and fill those areas with sand again.

Is this a common problem or an installation error? Does water get in on those spots more easily from outside the pool because the straps are attached there? Seems weird that the same sink hole is forming at the same spots all around the pool.

Your help/advice is much appreciated.

one other thing... i am concerned about draining the pool because it is sunk into the ground on one side a good foot and a half. Maybe by September that wont matter? I am concerned about the pool being damaged without the water weight.