On previous iOS platforms, find my phone would work sometimes. It hasn’t for at least the last two. Now it chimes for a split second and the message disappears. I have an iPhone SE currently running iOS 11.4.1. My Garmin device is a vivosmart hr+. I’ve played with various settings. From what I and some others have seen, it appears to be an app bug. I’m hoping someone will care enough to fix this feature, since it’s handy. My girlfriend has the same phone, but hasn’t upgraded to 11.4.1 yet. She has a vivosmart hr. Same issues. It works if the app is open and the phone unlocked. The message stays and the chime repeats. But when the phone it locked, it gets about three notes out and cancels.