App Store fails to find updates with error code NSURLErrorDomain error -1012

After upgrading from macOS 10.12 to macOS 10.13.1 (High Sierra), I get the error NSURLErrorDomain error -1012 when trying to update using "App Store".

Running software update from command line using sudo softwareupdate -l brings the same error:

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

Now looking at /var/log/install.log, I get the following errors related to a problem with the certificate from host swdist.apple.com and I can't find a way to solve this problem. Looking at the certificates in "Keychain Access", everything appears correct with default settings. I even tried to add the certificates from swdist.apple.com into Keychain but I keep getting the same errors. Any idea?

2017-11-14 21:59:33+01 gougnies softwareupdated[568]: Adding client SUUpdateServiceClient pid=98499, uid=0, installAuth=NO rights=(), transactions=0 (/usr/sbin/softwareupdate)

2017-11-14 21:59:33+01 gougnies softwareupdated[568]: SUScan: Scan for client pid 568 (/System/Library/CoreServices/Software Update.app/Contents/Resources/softwareupdated)

2017-11-14 21:59:34+01 gougnies softwareupdated[568]: Got status 200

2017-11-14 21:59:34+01 gougnies softwareupdated[568]: SUScan: Using catalog https://swscan.apple.com/content/catalogs/others/index-10.13beta-10.13-10.12-10. 11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog.gz

2017-11-14 21:59:35+01 gougnies softwareupdated[568]: Failed Software Update - Refusing invalid certificate from host: swdist.apple.com

2017-11-14 21:59:35+01 gougnies softwareupdated[568]: Product 091-16064 did not load successfully. Error Error Domain=NSURLErrorDomain Code=-1012 "(null)" UserInfo={NSErrorFailingURLStringKey=https://swdist.apple.com/content/downloads/53/53/091-16064/msgypzko1txpw90pyj6eq b4uf6ncak8igd/091-16064.English.dist, NSErrorFailingURLKey=https://swdist.apple.com/content/downloads/53/53/091-16064/msgypzko1txpw90pyj6eq b4uf6ncak8igd/091-16064.English.dist}