Hi Madhavan Menon,
Please check if the win10 1607 has installed the monthly rollup, if not, please install the latest monthly rollup manually on the win10 1607 clients, then check if they can update from the WSUS server:
https://support.microsoft.com/en-us/help/4000825
On the WSUS server, also check if it has installed KB3095113 and KB3159706(with manual steps), if not, install them to upgrade the WSUS server.
Best Regards,
Anne
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