I was wondering if it looked like it heaved under the bottom rail. There were some pics last year where someone had a wall that was heaving up like that and Dennis or someone had recommened scraping the area under the rail to level with an impliment (that pool was still full) and that pool wall had settled right back to straight after that - since this one is not full, getting it to level along there should not be hard. It may be just that one area?