AD health question - locked out of admin account

Question

DC1 - going to be decommissioned.

DC2 - Hyper-V VM 2016

DC3 - Hyper-V VM 2019 - operations master.

DC1 - unable to RDP into this DC using the account used as the domain admin, says password is incorrect. Can log in with same account locally/ RAID 1 is degraded so I don't want to stress it with a reboot unless I have to. Able to RDP into other computers using same account.

Took DC1 off the network. Rebooted DC2. Another server logged in as the the account being used as the domain admin gave a notification that account credentials have changed and that I needed to lock the user and log in again. I tried doing so and it said my password was incorrect. This was while DC2 was rebooting. This only occurred once. Putting DC1 back on the network and DC2 finished rebooting allowed me to log back in as the domain admin. DC1/2 were back on the network at about the same time so hard to say which fixed the problem.

When DC1/2 are off the network and I reboot DC3, it sometimes comes up as Network 3 instead of the domain network name. Disable/enable DC3 NIC when one of the others are up puts it on the domain network.

DC3 hangs on reboot when coming back up on Applying Computer Settings when DC1/2 are offline but comes right up when putting DC2 back on the network. Unsure if this is coincidence or not.

Microsoft AD replication status tool is discontinued.

repadmin /replsummary had no issues before I started testing. Showing errors after testing but my understanding is that it will show errors in the next 24 hours since I took them offline several times.

What can I do to check/restore the health of my active directory? I don't want to decommission DC1 until I know DC2 and DC3 are healthy. This will be my first time having an active directory where all my DC's are VM's. DC1 is a dedicated hardware DC.