Wsus server clients not updating
The issue is described here in a blog post which focuses on Windows 10 1511, additionally another KB article which is for 1607 describes an issue where you had synced updates prior to KB3159706 being installed.
We have to purge these updates out of the WSUS Database, which requires declining them deleting them and removing them from the DB using SQL Commands, once the hotfixes have been installed we can then download the updates again.
In this case, WSUS had clearly not installed correctly because a folder was missing from the server.
This folder contains a CAB file that any client downloads when registering to the server.
Whilst the information provided is correct to the best of my knowledge, I am not reponsible for any issues that may arise using this information, and you do so at your own risk.
This is nicely explained in a blog post from back in 2008!
If your WSUS is already in working order, your Windows 10 machines should be registering, but, will likely show no status for updates.
Just replacing that folder was enough to get the remaining Windows 7 clients talking to WSUS, however..
because of the number of updates each client has to process and a maximum of the amount they can process per detection you may encounter an issue in the log, WARNING: Sync Server Updates Internal failed: 0x80244010, the key thing to do here is increase your detection frequency on the clients to once per hour.
This includes /resetauthorization and /detectnow switches for the tool.