“Because these non-Gmail Google accounts aren’t actually a member of the Google organization, they won’t show up in any administrator settings, or user Google lists.”
An employee creates a Google account on a plus-sign alias of their work address, and Slack and Zoom treat it as a company login. Fire the employee and the side account keeps working, invisible to the admin. Google got the report on August 4, paid $1337 and pushed no fix in 134 days. The bounty cost less than the laptop the fired employee was supposed to hand back.