I had this issue yesterday, but after restarting Xcode it did work again.
Today I do have another issue:
ERROR ITMS-4088: "The organization <Name of Account> does not have permission to modify the application with the Apple ID 123456789. Please try again, using an account for an organization with access to this application."
at SoftwareAssets
I do have my own Account and I am also an Admin of an account of one of my clients. Before uploading the App, XCode clearly showed that it did use the certificates, Profiles, AppIDs, TeamIDs etc from my own account (which is correct), after uploading it seems to have tried to link it with the other account (which is not correct). Yesterday it did work fine with the same App and I never had any issue like this before.
Anyone else having similar issues and knows how to fix this?
And when I think of the "Transparency Issue" with the Marketing Icon (which I doi have with another App of mine, and which is also a big topic here in the forum), it seems that right now iTunesConnect is heavily broken.