I was editing a fairly big modal, on a fairly small page, which resulted in the modal going under the edge and not being able to edit the rest. One option to fix this would be to add an option to adjust the page height manually or automatically if you open the modal.
Sorry that you've run into this problem! As modals have position:absolute, they don't increase the page height and this defeats the way Bootstrap Studio's mechanism for increasing the height of the page preview. We will work on improving this for the next releases.
A workaround right now is to set a height to the body, making it tall enough to display your modal.