Cannot login to Forum after changing email

After changing my e-mail address on the account.qt.io Profile page I cannot login to the Forum anymore, although I can login to all other services: in fact, I am typing this issue using the same account that does not work on the Forum.

The error I get is:

Internal Error.

Oops! Looks like something went wrong!

/auth/QtAccount/callback

Email taken

I tried switching back to the same email address, and even to a different one, without results. Thinking that the change might still need to propagate somehow, I waited 12 hours before retrying, with no luck.