Blank Message from Unknown

I've had this happen to me for a few weeks now on my iPhone 6s Plus 64G: I'll randomly go into the message app to either text someone or look at my messages and I will see a mesage from "Unknow" with no text or anything- it's blank. I can click on it and it'll open the message, but still nothing- not even a blank bubble. If I click "details" ALL it says is "Stop Sharing Your Location With Unknown". I'll press it, but it wont respond. I'll delete the message and a few days later, it'll pop back up. What the heck is going on?