Issue was mentioned in this [meta topic](https://meta.discourse.org/t/send-a-notification-to-watching-users-when-adding-tag/125314)
It is working well when category is changed because NotifyCategoryChange job already got that code:
```
if post&.topic&.visible?
post_alerter = PostAlerter.new
post_alerter.notify_post_users(post, User.where(id: args[:notified_user_ids]))
post_alerter.notify_first_post_watchers(post, post_alerter.category_watchers(post.topic))
end
```
For NotifyTagChange job notify post users were missing so it worked only when your notification was set to `watching first post`
17366d3bcc