The beta only opens in first desktop space on OS X Catelina here. When having moved the app to another space the open dialogue box opens up in desktop one and not in the space where the rest of the UI is. Solution is to go to the first desktop/space and drag it over manually. Or just use AE beta in desktop 1.
The public build respects the os settings which is nicer to work with and why I suspect that this is a bug.