How to trigger notification on watcher's comment?

[Dimitrios Danampasis]

We are using Jira Server on-prem, in particular the JIRA Service Desk product. When a watcher is either commenting on an issue or just tagging(mentioning) the Assignee, the Assignee never receives a notification email. When comments are being made by others, the Assignee is receiving emails. The project, under which the issue is found, is using the Default Notification scheme meaning that the proper permissions seem to be in place. Upon Issue commented the following will be notified:

• All Watchers
• Current Assignee
• Reporter

I will need to notify the Assignee, no matter who is commenting. I would welcome any help in this matter. Thanks in advance.