it looks like not all preview bugs have been ironed out yet, at least in this sample design: http://ovh.to/jAvufC7 where the image cover is rendered fine in the browser preview but not inside bss where a white bottom margin is added.
Thank you for starting this thread. I replied to a similar report yesterday, but to recap, the issue is that Bootstrap Studio expands your page preview in the app to match the page height. So if you set some element height to 101vh, your body will expand to more than the preview, then the app will increase the preview and the process will repeat to infinity. This is why we convert vh units when displaying them in the app (exporting and browser preview are not affected, only what you see in the app).