This doesn’t help with the problem, but might deepen your understanding: Xwayland is the X server.
Xwayland is also the Wayland client that uses Wayland to connect to mir-kiosk. Other Wayland clients (e.g. those in mir-kiosk-apps) respond correctly to the display configuration messages sent by mir-kiosk.
This problem lies somewhere between Xwayland, the Window Manager (i3) and the X client (chromium). At least one of them is doing the wrong thing.