My base cluster on my 2014 did that with the MPH part. I believe the little gears inside it goes bad. I just swapped my cluster with a Premium one (with the proper tool), and now the old one just sits in my closet.
I even tried opening it, readjusting it, but after a day or so, it would fall back below 0.
You COULD take off the glass cover and tape/glue something right under the needle to MAKE it only go as low as 0 MPH. That would fix it in a ghetto way. LOL