I use SSL for the Stacks4Stacks website and all my RW addons (themes and stacks) are tested and confirmed to work with https protocol websites. It’s the normal thing nowadays. If you go to the Playlister webpage you should see it loads with a green padlock icon and the Playlister stack works.
Perhaps that’s the reason it doesn’t work for you? Cross domain calls that are insecure or references to files on a password protected directory that you can’t access without being logged in?
Unfortunately with no link, you’ll have to do some of the legwork yourself and check the web browser developer console and the server error logs to see what’s going wrong.