FogBugz stopped pulling emails. The error/notification stated a confirmation was required and that we needed to press "Start downloading messages now". Once we pressed that button all the emails started to be processed again for our one mailbox in FogBugz.
To check error/notification navigate to:
FogBugz Avatar Menu > Account/Settings > Mailbox - then EDIT the configure Gmail account.
Manuscript has not started downloading messages from this mailbox because it contains 3 messages.
You can download the existing messages, but keep in mind that Manuscript will create and send email notifications and auto-replies for the messages downloaded. Consequently, you should make sure that the mailbox only contains new, rather than historical, messages before proceeding.
"Start downloading messages now"
Gmail account in FogBugz.
FogBugz Admin account.
For some reason, Gmail will sometimes not recognize an otherwise valid username and password. Sometimes this apparently happens when an account is signed into from another browser but sometimes it seems completely without cause.
When FogBugz sees errors of this nature being returned from an email provider, in order to prevent being blacklisted by that provider it stops checking for emails and notifies the administrator that there's a problem. That allows site admins to update email account usernames and passwords when they need to be updated (which is easy to let slip through the cracks but seems not to be the case in your situation) before telling FogBugz to resume checking emails.
If you come across this problem regularly please refer to Google Support Document Troubleshoot problems: I can't sign in to my email client.