Resurrecting an old thread because just today and FOR THE FIRST TIME EVER -- my Series 1 watch (running Watch OS 3.1.1) And my iPhone 6s Plus (running iOS 10.2) stopped pinging my phone!
I toggled Bluetooth off and on, and then it worked... but ummmm... can't do that every time if I don't know where my phone is!!!
Anyone else having recent problems with this?