I don’t know how your microwave is mounted, but I had a similar issue in my 2020 International. We camped in a remote area of a state park and the road to the campground was rough. When we arrived, the microwave was completely out of the cabinet and the trim ring was destroyed. The microwave was also destroyed.
I ordered a new microwave and trim kit. When I installed it, I found that Airstream neglected to install the base plate that not only supports the microwave, but it directs cooling airflow from underneath the unit out through the vents in the trim kit. Without this base, the four tiny feet that support the microwave were balanced on a little thin strip of wood. Once the road got rough and the feet slipped off of the wood strip, the flimsy metal trim ring was the only thing supporting the microwave. That didn’t last long.
The problem was solved when I properly installed the microwave. I don’t know if Airstream left the base plate out by accident, or if the installer was just lazy and didn’t want to bother installing it.
Current: Newmar Ventana 3715 (6,265 lbs. cargo capacity )
Past: Airstream International Serenity 23FB