Our Monterey did that when only a few months old and it happened slowly while parked in storage; a slow leaking corner airbag didn't help. I learned not to twist the body during air leveling, and to store on relatively level ground with air dumped.
But the main cause was found when Monaco warranty service in Coburg found the windshield hadn't been mounted properly at the factory, which mirrors Keith's experience. I've yet to hear of a bad experience by way of RV Glass Solutions, and have recommended them here with great results.
Joel