I plugged my 950 XL into my dock the other day and tried to play some music using Groove, it went through each track of an album in a few seconds and then announced that it couldn't find my playback device.
So I checked every setting I could find, then checked all my cables and connections, no luck.
Luckily my wife has a 950 with dock so I checked hers, all working, then checked her phone on my dock, again all fine, finally I checked my phone on her system, no luck, so I figured it was my phone.
Did a hard reset, re-installed all my apps, tested everything and finally plugged into the dock and fired up Groove, all OK now.
Thankfully it is a bit of a doddle to get up and running again on a PC or phone after a reset with cloud based computing.