Years ago, when I first installed a pool, I taped a hose to the top rail while it was filling. Everything seemed just fine. The water ran all day and the tape held the hose in place just like I wanted it to. Well, we went to bed and let the hose run and got up a couple of times during the night to check on things. One of the times we checked, the tape had popped loose and the hose had fallen to the ground and was aimed right at the base of the pool! It had washed out a "footprint-sized" area of sand about 2-3 inches deep. I was so bummed out; my brand new pool wasn't gonna look perfect! But, it never got any bigger. I just told the kids to leave the "footprint" alone when they were in the pool and they did.

I replaced that liner about 7 years later and the footprint had never gotten any worse. If our installation people don't have any words of wisdom for how you can fix this, at least maybe you'll have the same luck I did with my washout.

Good luck and also welcome to the forum!