For me everything have been installed successfully... And even more... December's SSU has been successfully installed two times... [SPOILER]
For my case, i was NEVER be able to install any .NET update... But all other update (SSU and cumulative update) has been successfully installed....
OK... But that don't help me... Is a complete reinstall of .NET needed ?
And... that dont work... And... UX Theme was broken, YES ! Wait ! The error code is not the same... [SPOILER]
KB4556399 failed again... With the tool... And BypassESU-v7 [SPOILER]