Symptoms : Users don't receive any notifications about updates on their ticket.
Cause : They might have accidentally or willingly clicked on "Turn off this request's notifications" in email.
After clicking on this, a message will be displayed to the user, stating that they won't receive any updates on this ticket from now on.
Solution : To turn on the notifications again follow these steps:
Step 1 : Go to your ticket following the link in email.
Step 2 : Click on "Get Notifications". Refer image below.
The customer will start receiving notifications on updates of the ticket after that.