Had same problem with same phone. Worked on Wife's 640 but not mine. Finally set up new Microsoft account and wiped phone to sign in with new account and it worked! Upset that I had to move everything over to new account just for the band.
I had same issue on my Windows Phone. It worked on my Wife's same exact phone but not mine. Set up new account and signed into Health app with new account and worked! Not happy but at least it works now.