Single contact no notification of new messages received, why?

[Android Central Question]

Have a single contact that I don't receive notifications for new messages. There is a bell symbol with a diagonal line across it, A backslash.

All sound and message app setting have been checked and nothing has changed. What does the symbol represent and how do I correct this?
No new apps, Samsung Galaxy S8 plus. No new updates I am aware of. Running Marshmellow.

 

[B. Diddy]

Welcome to Android Central! In your messaging app, open that contact's message thread, tap Menu, then People & Options, and make sure notifications are turned on for that thread. You can mute specific threads in most messaging apps.