GitHub oAuth just gives me "Forbidden" when logging to Gerrit

Hello, I have two Gerrit accounts: "osvoboda" (primary e-mail: osvoboda(a)redhat.com), which I use exclusively, and "lenoch" (primary e-mail: ondrej(a)svobodasoft.cz), which I must have created because of my issues below, perhaps hoping to somehow merge the accounts later or just "make it work" cluelessly. I would like to use my GitHub account to log in to the "osvoboda" profile. When trying to add a new identity and clicking on "GitHub OAuth2 (gerrit-oauth-provider plugin)" I am able to log in to my GitHub account and approve "oVirt Gerrit", which then shows in "Authorized applications" in my GitHub settings. Trying to log in, however, gives me a simple "Forbidden" message. Can anyone help me troubleshoot this, please? I thought this had to do something with the e-mail address GitHub supplies to Gerrit through OAuth, but I can never be sure. Do you know what "public information" GitHub actually shares with Gerrit? If anything, I wouldn't mind to have my "lenoch" Gerrit account removed, if there was any clash with the "osvoboda" account, in terms of linked e-mail addresses and GitHub authorizations. I hope someone has a clue :-) Thanks, Ondra