Recently purchased Lumia 950 XL. Got frozen/rebooted 2x in 3 weeks... not too bad. Major problem - and possibly reason for reboots - is unreliable Bluetooth. Both freezes have happened while I was trying to make one or the other BT device work.
Jabra Tour - connects, but randomly disconnects and reconnects. Sometimes doesn't connect at all. Turning BT off and back on in Settings or restarting phone helps... but only that much. Works fine for a while, from time to time.
Jabra Classic - same but actually even less reliable. Less working, more disconnecting or not connecting at all..
Fitbit Charge 2 - mostly works, maybe once in a week refuses to sync, even if it is showing connection (phone can see tracker). Works after phone's restart or toggling BT in Settings.
Most ironic part? - old BT headset for PS3 (!!!) seemed to work fine. Well, for a few days. Then headset died. Not related to phone, it just... died. So the working phase might have been coincidence, or that thing was one of rare BTs actually working with 950 XL. Maybe I have faulty phone, but I did come across numbers of people complaining about same BT symptoms, so unless it is batch problem, looks like BT is just infamously unreliable at this stage. Which is, like, 16 months after phone was released. I know Win 10 Mobile is not a priority for Microsoft, but still... they should show a bit more pride in what they do, even if it is not as successful as they were hoping for.