For server owners!
This is probably because their verification link has expired. The default timeout is one minute. The web portal will display success, but the Discord side of the bot has stopped listening to the web side for this user. They just have to leave and rejoin or run
dc.verifyagain to get instantly verified without clicking the link.
It probably means the staff member shared their verification link as an example to someone who needed help. Verifications links are private and should never be shared to anybody. They are unique to each other and opening them in any browser will link it to this account. This is done locally and we cannot roll this mistake back. Make sure you only click your own verification links and never share them with anybody.