Ah the dreaded error that WSUS throws at you.
There are several "solutions" to be found with a quick Google.
But in my case it was quite clear, on 5 identical machines 1 couldn't access the WSUS server on the network. So what's the difference?
Came across this post on docs.microsoft.com
https://docs.microsoft.com/en-us/troubleshoot/mem/configmgr/troubleshoot-software-update-scan-failures
The portion that stood out was the proxy bit. Checking the current settings on the machine that was working and the machine that wasn't working.
The working machine:
C:\windows\system32>netsh winhttp show proxy
Current WinHTTP proxy settings:
Direct access (no proxy server).
And the non working machine:
C:\windows\system32>netsh winhttp show proxy
Current WinHTTP proxy settings:
Proxy Server(s) : http=proxy.domain.lan:8080
Bypass List : *.domain.lan;192.*
