I ran into this problem last week on Win10 when I had to fire up a linux VM to do some troubleshooting for work. Found the answer in the VBox forums, and saw the same thing in the forums a couple of times in previous years.
I was lucky in that there were new builds to download (I don't use it often), but the answer for each of the forum threads was "wait".
On a tangent, this win10 box is my gaming box, and I haven't changed any of the settings regarding updates - it's just stock win10 stuff. Which is amusing when win10 gives you the "we're rebooting, you can either do it now or in 15 minutes" bit (different to the 4-hour delay option). I've come back from dinner to find the machine freshly rebooted. :)
I was lucky in that there were new builds to download (I don't use it often), but the answer for each of the forum threads was "wait".
On a tangent, this win10 box is my gaming box, and I haven't changed any of the settings regarding updates - it's just stock win10 stuff. Which is amusing when win10 gives you the "we're rebooting, you can either do it now or in 15 minutes" bit (different to the 4-hour delay option). I've come back from dinner to find the machine freshly rebooted. :)