WSUS Strange Issue

[ITGURU]

I've got a strange issue with windows 10 and WSUS.

 

Clients were on 10.0.17134.471. I approved the 2019-12 cumulative update which should take the build to 10.0.17134.1038

 

Some clients have downloaded installed the update and showing correctly in WSUS and now shows 7 updates required.

 

However, there's areclients checked in today showing still as version 10.0.1734.471 with 11 updates, however when i check the updates required, all the updates show as 'not approved' and doesnt list the 2019-12 cumulative update, but does list all the other months 2019-05, 06, 10, 11 for version 1803.

 

All machines were initially on same windows 10 1803 build, so why do some machines need 2019-12 update and others not?