The problem has to be with Windows 10, not the Band. I never had a problem with my Lumia 920. Within a day or two of getting the 950 the problems began.
For a couple of weeks I could reestablish connectivity by simply going to the Health app and forcing a sync. But that stopped working too. Then I got the OS update and it seemed to fix the issue. Things were good for a couple of days and now it's back to the same crap. Restarts, deleting Bluetooth profiles, forcing syncs, none of it works.
So my Band is stuck working as a fitness tracker and nothing more. More than anything this is eroding my positivity towards the platform. I have to imagine that people within the halls of Microsoft have been experiencing these very issues. How fixing interoperability between Microsoft's own devices hasn't been prioritized is beyond me.