I'm not experienced with these showers, just sharing my personal experience. One of the showers in my house had this problem, and the HOA said it was common in our complex because the builder didn't correctly attach the panels to the wall. They didn't use enough adhesive and didn't brace them as the adhesive was drying. So ~5-10 years after they were built, many started doing exactly what yours is doing. The HOA said they would keep pulling away more and more, and could possibly completely fall off. If this is indeed the problem, it's not a hard fix. Get the right adhesive, apply plenty to the panels, and brace them with 2x4s at several points. Let it dry for at least as long as the adhesive recommends, and you should be good.