Xcode export/upload error: Your session has expired. Please log in

The session of one of my accounts (not even the one I was trying to use) had its session expired. This seems to be new. I just had to re-sign in to the errant account in Xcode > Preferences > Accounts.

I had the same problem.

Solution: Go to Xcode->Preferences->Accounts and make sure that ALL your accounts are connected. If you have several accounts and only 1 of them is not connected you will always get the error, no matter for which account you want to do stuff/export/etc. So make sure ALL accounts are connected without exception. You see a lightning icon next to your accounts that are not connected.

Hope it helps other ppl :-)