I ran into the same exact problem.
My Band had been connected to my old phone when I linked it up to the 950. It seemed to be working yesterday but this morning I found that despite the devices being paired and connected they couldn't sync. Deleting the Bluetooth profile fixed that problem.
But then I noticed that I wasn't receiving notifications for texts or calls. Although I could still type a message the recipient never got it. I fixed that by going into the health app, removing all the tiles on the band and adding them back. So now I get notifications for everything and can send texts again.
Unfortunately, I've found a new problem. I get notified about incoming calls, but the phone disregards the command to ignore the call. It keeps ringing.
I'll have to try reinstalling the app, but it's extremely frustrating that the Band isn't working properly with the 950. The Band worked flawlessly with my old 920. Why are these two brand new devices having so much trouble?
I keep coming across way too many of these odd little glitches. I'm left wondering when we can expect some updates and if we're going to be stuck waiting on AT&T to approve every little thing.