It happened when I tried to put an HtmlView on top of a Listview on the screen design. It did not occur right away, but it always happened while I was working with these elements. When it happens the screen design goes blank so there is no way to, say remove the html or the list. I also noticed that as soon as I added the htmlview on top of the listview, the keys for the next screen go blank (however if they are already in use the app will still use them).
I'm using SUP 2.1.0 and this has happened to me twice now (both times were as I described). The first time I just decided to try rebuilding the entire workflow, but then it happened again. Any help would be much appreciated.