First, I tried opening File>Recent>my drawing and I got the same problem of a small square with my drawing in it (as before).
Then I just went to open and opened the Artstudio file that way. I worked on my drawing and everything seemed to be going good and then the layers started acting up. Some would disappear and then re-appear. This went on for a couple of minutes and I got to a place where I could save the drawing and exit/quit Artstudio Pro.
Scary. I thought I had lost parts of my drawing. The layer area has something going on that is causing layers to appear, disappear and looks like, move into Group layer. When the Group layer would be selected, the layers would all appear again.