My Lumia 950 XL appears with a yellow exclamation mark in Windows 10 Device Manager and Windows is convinced that it cannot find a driver for it. Oddly enough the connection did work a week ago. What am I doing wrong and what happened to the driver?
You can try to install the Windows Device Recovery Tool. This should automatically install all required drivers for your phone.
I had a similar issue after Win 10 anniversary update. Plugging phone into USB 3 hub would not recognize the phone (even though it worked before the update). I tried plugging it directly into a USB port on the MB and it recognized the phone, installed the drivers, and connected. AFTER this, I was able to connect via the USB 3 hub, as I had before the update. Hope this helps somebody.