The bug was mentioned on meta https://meta.discourse.org/t/users-are-seeing-handling-of-unhandled-tag-again/155367
It was related to users who are watching a specific topic. In that case, when the hidden tag was added or removed to the topic they were notified by `NotifyTagChangeJob`.
That job should take hidden tags into consideration. If all changed tags are in a hidden group, it should exclude user not belong to that group.
At the same time, if visible to anyone tag is added or removed users watching topic should be notified.