in Vaadin 10.0.1, rotating the screen on a mobile device is not working well
I tested one application made with Vaadin 10 on my Android device, and when I have screen rotating enabled in my Android, it rotates well, and I do not see similar issue than you. So, I tend to think it is not happening due Vaadin 10.
Note, when you install PWA on your home screen, the manifest will define whether it keeps the app in portrait / landscape despite the rotation setting of the device (the app will be still rotated when run in browser)
https://stackoverflow.com/questions/47054223/pwa-orientation-change-off-for-polymer-apps