So in the most recent release of Power BI Desktop, I've encountered the same issue several times.
I go to Publish a report and I get a login popup. This login popup and publish are happening at the same time, and I can't log in and the report publish never happens. I end up having to go to Task Manager and end the task. Luckily Power BI has the autorecovery, but this is very annoying.
I have also received this error after I've already logged into Power BI Desktop. The popup doesn't happen all the time and I've still been able to publish some reports, but it has happened multiple times now.
I'm wondering if it's a bug in the newest release.