@brianmcdonald, I realize you may not have the same setup, but I too had a situation when the setup looks good, but on re-click “pop3 polling enabled” it gives the “POP3 authentication failed” error.
I have a https only site setup with Google Authentication working on a different machine a few days ago. Today, on a different server with same setup, something seems to have changed on the Google side. When I re-click “pop3 polling enabled” it gives the error "POP3 authentication failed. In the inbox of the POP3 account I was using, I received an email from Google containing this message:
I clicked the “Learn More” Hyperlink and it took me to a place that lets me configure the POP account to use “Access for less secure apps”. After I turned this radio button to “on”. Authentication worked.
https://support.google.com/accounts/answer/6010255
