I believe you have already tried signing out of Muse and CC and then signing back to CC and open Muse , if not then please try this on first place.
In case you are selecting any data center while publishing , please try to change the data center and then check.
Does the same happens with any site and all sites ? Try to create a single page new site and publish to BC as a new site , also try to select any listed site under options menu and then proceed to publish , check both conditions if that works.
Still problem , then Go to Edit Preferences > Publish account and check the Adobe ID used for publishing your site to BC , validate if not correct.
If you are using multiple Adobe ID , then try with any other Adobe ID in preferences publish account and then check.
Thanks,
Sanjit