Are you signing in with the same credentials with which you bought Stardock apps?
I have a Wincustomize login that I've been using for years. It is slightly different from my Stardock account login.
EDIT: Bingo! Just tried logging in with my Stardock login and downloads came up just fine. For some unknown reason my Wincustomize login was logging me into the site but not giving my the ability to download anything while my Stardock login both logs me in to Wincustomize but also lets me download as normal.
Don't know what changed re my old login and site privileges but I'll change the login in my password manager and, hopefully, all will go back to normal.
Give the man a chocolate cigar! Thanks for bringing up the idea that it might be the login.