I have tried manually installing KB3172605 July 2016 Rollup to speed things up, but a window dialog saying 'Searching for Updates on this Computer' andit just hangs searching forever.
This list of updates have been expired for Windows 7/Windows 7 64 bit/Windows 2008 R2 on January 12, 2017.
This seems to have fixed the slow scanning without the need for manual installs up front like KB3020369/KB3172605
They are old updates which already superseded by various updates before 2016
what @ch100 mean is that their metadata is removed and no longer pushed to WU/WSUS
and they are not available for download anymore in MU catalog
I copied the KBs manually from the report, few of them apply only to 64-bit version, which means Windows 7 64-bit and Server 2008 R2.
Also when updates are expired, they automatically move into the Declined section.
If you are interested in understanding WSUS better, check for anything written by Lawrence Garvin anywhere on the Internet. He sadly died unexpectedly not long ago.
But if you check either WSUS or Microsoft Catalog, you will actually see the relationships between them.
I briefly checked and I found that there are few of them being part of longer chains of supersedence, some of them in the middle of those long chains, some superseding each other.
The net effect of expiring updates belonging to longer supersedence chains is that the calculations performed as part of Windows Update by svchost.exe are much lighter and as such the performance is dramatically improved.
Saying that, you would still be better off by installing an optimised Windows Update agent like the one contained in KB3172605 or if you don't trust some of the components inside, then the next best is KB3138612, but this is not as good as KB3172605.