Can you check if screenOrientation parameter is firing with mbox call on given page? Also screenOrientation seems to be an custom mbox parameter so mbox implementation should be in such a way that when you toggle the mode the target call should fire with the exact screenOrientation then only target would identify and deliver the experience.
Thanks for reaching out. Not sure if others have an alternate solution, however I'm curious to understand why the screenOrientation is not working as expected. Are you testing in a mobile app or a browser on iOS? Do you have a URL I could test?