I have experienced the randomness of this issue even with the latest v6. I have deduced that the software loses rights for full control or to edit the "Releases" folder. For a workaround, create a new folder anywhere that is higher up in your drive, not under the mastering project at all. Once that folder exists, browse to it and select it as the destination of your digital release files. Voila. The contents in that folder behave normally for me. I can run the digital release the way I like it configured with the check boxes and switches, AND it produces the output files just as expected. It is my best guess at what is causing it, and the workaround has worked reliably for me. New folder outside of your master project song folder, and run to that as the target destination of the digital release pathway in the popup. Good luck everyone!
Arthur