Apache 2.4 is unkillable and can't be stopped on Windows Server

OK, so I think I was on the right track.

After searching on the Web about the recently installed updates, the KB4338818 is the one causing problems.

This is happening for other softwares, like FileZilla Server, as detailed here.

I've just uninstalled this Security Update and now Apache can be started/stopped as normal!

So I hope Microsoft will fix this in a later update!

Microsoft is releasing KB4345459 to fix the issues in Windows 7 and Windows 2008 Server.

https://support.microsoft.com/en-us/help/4345459/stop-error-0xd1-after-a-race-condition-occurs-in-windows-7-service-pac

Seems like Microsoft is starting to fix the issue, until now only for Server 2016 and Windows 10: https://support.microsoft.com/de-de/help/4345421/windows-10-update-kb4345421

KB4338831 seems to fix the issue for Windows Server 2012 R2.

This non-security update includes improvements and fixes that were a part KB4338815 (released July 10, 2018) and also includes these new quality improvements as a preview of the next Monthly Rollup update. Source: July 18, 2018—KB4338831 (Preview of Monthly Rollup)

It's available as a recommended update on Windows Update.