There is an issue right now in Garmin Connect that affects the 230, 235 and 630 watches. I think I've seen the same behavior on the Vivosmart HR as well. When you go to the device settings (either on the web page or on the mobile phone app) and change from miles to kilometers and save it, it will not get recorded. So every time you get back to that menu it remains in miles.
This results in that every once in a while the watches get changed from kilometers to miles. This is not happening to other models, such as the Fenix 3.
