Checking MacOS updates failing with "The operation couldn’t be completed. (NSURLErrorDomain error -1012.)"

Since a couple of weeks, checking for updates on my Mac mini 2018 (our build server) is failing. In the UI it just tells me there are no updates available. Which is tricky.. and not true. I am on Monterey 12.2.1. The current release is 12.4. When I looked into this issue I found in the /var/log/install.log: (appendix 1)

Note several occurrences of:

2022-05-27 16:12:11+02 FoxtrotBuildServer softwareupdated[291]: Failed Software Update - Refusing invalid certificate from host: swscan.apple.com

in this log. Should I check for invalid certificates in the KeyChain? Which certificate should I check?

Running it from a command window shows the following:

FoxtrotBuildServer:s foxtrotbuildserver$ sudo softwareupdate -l
Password:
Software Update Tool
Finding available software

The operation couldn’t be completed. (NSURLErrorDomain error -1012.)

FoxtrotBuildServer:s foxtrotbuildserver$ 

The 1012 error seems to indicate that the url has been requested too often in a certain time frame. Which could be caused by the fact that I work in a big company and many devices (including Macs) share the same external ip-address.

When I try to load the failing url in Safari or using wget on that same machine it loads just fine. And quickly as well.

I do want my machine to get updated a.s.a.p. I tried downloading a full install for Monterey 12.4 and install that. That ended after a few minutes with a general error message telling me that the installation failed. In the install log I saw it was trying to access that same url and also failing.

My question is: what is wrong? What can I do about this? How to update my Mac to the latest version of MacOS?

I should add the the Mac mini is located in a remote and hard-to-access data center. That limits my options.

Please suggest..

Thanks and best regards, Frans