Recently, while setting up a personal MacOS VM using OSX-KVM, I came across an error trying to sign into the Mac App Store and iCloud saying "Validation Error. There was an error connecting to the Apple ID Server".
Many existing threads related to this issue, such as on the tonymacx86 forum, instruct you to make sure your ethernet device is on interface
en0, but this was already a thing for my Virtual Machine, so I had to look elsewhere.
Thankfully, "jwegman" from the Unraid forums has instructions for a fix.
Basically, you need to replace the model type
e1000-82545em, which makes Apple load a different Kext for intel ethernet devices.