Full Disclosure: I'm not sure this is where I should post this.
I may have uncovered an issue with the Atlassian SSO engine.
I work with JIRA during my day job. I log in with my work email.
I log in to Community with my personal email.
Until recently (I only figured out the potential source of my login problems a few minutes ago), that was not a problem.
Whatever site I log in to first thing in the morning will hold the credentials. Meaning if I log in to JIRA first, Community will try to use those credentials to log me in, and vice-versa.
I figured it out by clearing my cookies in Chrome while I was logged in to both sites. I then logged back in to Community, followed by JIRA. This resulted in JIRA not giving me access to any of my projects because it saw my personal email credentials, which don't hold any rights on JIRA.
to further my point: the only way I got Community to allow me to post this very discussion was to go through Incognito mode. Otherwise, it would ask me to fix a "highlighted error" I couldn't see.