Microsoft has released Microsoft Update KB3189866 for Windows 10 Anniversary Update at September 13, 2016. This cumulative Update shall fix several security issues and shall improve Windows 10 (see Update KB3189866 shifts Windows 10 to Build 14393.187). But it seems that this update is causing download hangs on many systems.
Then the download hangs for hours at 48 %, 95 % or other percent values. I’ve a test machine, that hangs after a reboot at 45 %, 49% and so on.
My (failed) attempts to fix
First of all I tried a reboot, but the update process stucks again at 45 %. Then I read in a German forum, that a missing Defender signatur update could be a show stopper. So I opened the Defender windows via taskbar, went to Update tab and started a manual search for updates.
As shown in the (German) screenshot above, there was no new updates. So this attempt failed. My next attempt was to use the Windows Update Troubleshooter. I downloaded WindowsUpdateDiagnostic.diagcab from this Microsoft web site. After execution, the tool reported no problems.
After all Windows Update reported an error 0x8024001E. So I stopped Windows Update service and deleted the Windows subfolder SoftwareDistribution\Datastore. But that did not solve the issue, the auto update hangs again at 47 %.
Manual download and install fixed the problem
After many tests I decided, to use Internet Explorer 11 in Windows 10 Version 1607, go to Microsoft Update Catalog and download update KB3189866 for my 64 bit system.
After downloading the update package, I double clicked the .msu file and let Windows 10 install the update. This was successful at least.