Pool removed 4 yrs ago, very soft ground in that area. Is this a red flag?

We are currently looking at a home that had a pool in the backyard taken out 4 yrs ago. You can still tell there was a pool there and the ground is very spongy. We are a little concerned about this as we really liked the home and wanted to place an offer. Was the space not filled in correctly or is this a non concern/easy fix?

Re: Pool removed 4 yrs ago, very soft ground in that area. Is this a red flag?

Why don't you find out if the seller has documentation they can provide about when and how the pool was filled in, who did the work, if permits (if necessary) were obtained? If it's a concern, that would be the first step I would take (if you were my client). If you get more info, your concern may be alleviated.