no text tone from single contact

I have sevearl people with whom I exchange texts on a daily basis, and until recently, have not had any issues. However, a couple of weeks ago, I stopped receiving a text tone when I get a text from one of those contacts. Nothing has changed and I receive text tones from other people as well admin texts from school, Amazon, etc. Only texts from this one individual is affected. I have tried changing the tone but it makes no difference and I can't seem to find any record of other problems like this when it's only a single contact. Appreciate any suggestions.

iPhone 6+ 64Gb, ios 8.3