This is pretty common to AS Shower doors. To much weight and the door drops. There isn't a missing shim but it is easy to put one on each side. On my one warranty trip I had the service dept at JS put in a shim on both sides. They know exactly what is needed. May want to call and see if they can send a pair to you. They screw into the side wall of the shower.
In the meantime stop at HD or ACE and find a couple of nylon wedges. Forgot what dept I found them in, but they worked as a temporary fix.
2020 Classic 33 Twin, 2019 Ram 3500 Longhorn, ProPride