Most frequently used contact is muted but mute isn't checked, how to unmute/demute?
I had the same exact problem. I pocket muted my girlfriends notifications. I found the solution however! Go to your messages with the person who has a mute symbol next to the conversation. Then look at the spot that had their name at the top left (with a phone number right under) click the drop down arrow on the right side of the name. And it will say notifications. Then click on. (: good luck. (Galaxy s6)