I've been experiencing the same issue ever since switching to Win 10 Pro. Sound drops unexpectedly. Win7 Pro worked without a glitch.
This can happen while I'm streaming from the Inertnet or while I'm using VLC to watch videos, so it doesn't seem to be a browser issue. The only way to restore sound is, again, reboot. When it's happening with a web stream, the video stops there and then, and no other video can be started. The system might work for two weeks without problems, or the sound might again disappear a couple of minutes after reboot.
Last time this happened I tested the laptop's in-build speakers. Those made a noise, so assigning Windows sounds to in-built speakers seems like a valid option. In app volume and device preferences I can assign other applications to other sound devices, but Windows system sounds only allow Default, see attached.
Any ideas where the heck should I look next?