I just purchased a Microsoft Band yesterday, and after I set it up with my Lumia 635 with Windows Phone 8.1, I found that the watch kept disconnecting from the phone's Bluetooth, but it only temporarily reconnected when the Microsoft Health app was syncing with it. I've also noticed that there's no Missed Calls tile on the watch.
I've tried resetting the watch multiple times with the same result. I've also tried setting it up on an Android device, and it actually status connected and shows the Missed Calls tile.
Is there something wrong with the phone or perhaps the watch that I must be missing here? Thanks!
Also, I should note that in the setup process, the Health app did not ask me if I wanted to allow the watch access to notifications.