It appears that some users are unable to login to the platform at the OAuth stage. All users reporting this issue so far have pre 2006 accounts: DESiegel, Gamaliel, Pajz.
Hello! User:DESiegel on en.Wikipedia tried to sign on with the single sign on and received an internal server error, preventing them from signing up on the new process. This is the error they receive https://wikipedialibrary.wmflabs.org/oauth/callback/?oauth_verifier=3cd3782482fa177c8d16e0abc8aa58b8&oauth_token=5222cbd429cf8928dc9cff009a5ba9f4
Relevant thread on their talk page: https://en.wikipedia.org/w/index.php?title=User_talk:DESiegel&oldid=789850955 the thread is WP:Newspapers.com
Can someone take a look at this? Thanks!