Domain is 2019 and at the highest level for domain and forest.

I’ve installed a brand new Server 2025 Datacentre VM, activated it, ran Windows Updates, all good.

Joined the domain, all good.

Login to the VM with the Domain Admin account, all good.

Can reboot as many times as you like, and login fine, no issues.

Added the AD DS role and promoted to a DC.
Reboot
Cannot login, I am told the username and password (same domain admin account) is incorrect.

After a frustrating afternoon I’ve now just spun up a brand new 2019 Datacentre VM and gone though all the hoops. Promoted to a DC. Rebooted. NO PROBLEMS whatsoever.

So…I can add a 2019 DC into a 2019 domain and have no issues, but if I do it with a brand new 2025 DC I can’t then login at all.

Have I missed or overlooked something?

My next test will be to upgrade my fully-working 2019 DC VM to 2025 DC and see if it upgrades okay and I can still login. Will report back