For Windows 8.1 manually download the Servicing Stack. Then check for updates.

 

https://support.microsoft.com/en-us/help/3173424/servicing-stack-update-for-windows-8-1-and-windows-server-2012-r2-july

 

Check the Prerequisites. Download and install the 2014 rollup if not done.

 

Then download the August 2016 rollup if you cannot get updates after installing the above servicing stack.

 

https://support.microsoft.com/en-us/help/3179574/august-2016-update-rollup-for-windows-8-1-and-windows-server-2012-r2