@Sebastian-Roth Just an FYI, I ran into this again on different hardware. An HP Z2 G4 Workstation did the same thing.
There may have been more to it though, still troubleshooting a bit. My failsafe in the postdownload script to have it still join the domain through the unattend file was injected into the file, but the computer did not join the domain through that method, there may have been a different reason for that though.
Point being, there could be other hardware that weirdly doesn’t get all the variables. I sadly can’t super test on this hardware as I discovered it when imaging a production machine that I can’t take out of production for testing. But I can probably find a chance to get the fos level device info or something.