When you are the owner of a ticket, you automatically follow it. As this is a predefined behaviour and to avoid the view becoming bloated with every ticket a user is assigned to, auto-followed tickets from ownership are tracked separately on the backend, which is why they don’t surface in the “following” view on the left.
The Actions menu shows the same “Unfollow ticket” label regardless of whether the follow came from ownership or a manual action, which makes the two states look identical when they aren’t.
Due to this situation you have to manually unfollow and re-follow the ticket if you re-assign it without losing track. As your action menu stills shows “Unfollow-ticket” in this case, confusion raises.
This is already known and acknowledged be the hubspot developing team.
Therefore, I’d like to advocate for an UI change — either a different label for auto-followed tickets or an option to convert an auto-follow into a manual one.