can't change preview to "devicd"

Hi, ​@tao li. Thanks for your post - that seems unexpected.

What happens when you click on the mobile icon? Does it change the setting but not update the preview, or does nothing happen at all? I’m wondering if the width and height being set to 0 is causing an issue. If you change the viewport option to something else, then change it back to Fullscreen, does it update the width and height and allow you to the preview to mobile?