I'm having an odd issue after having to rebuild my VCSA that crashed. I did a fresh install for stability, and am simply trying to add my hosts to the vCenter as usual. Relevant info:

- All systems have static IP addresses, are on same subnet, can all communicate.

- No firewalls or other traffic filtering inbetween. 

- Credentials are 100% correct across the board. 

- DNS is working between all hosts (host to VCSA, VCSA to host)

In my VCSA I go through the Add Host dialog as normal. I add the host using FQDN, give it credentials, it connects to the host and gives me the host summary correctly (showing ESXi version, Virtual Machines w/names, server model, etc). This tells me that the credentials are correct - it pulls all of the info as it should. I then assign the license normally, Lockdown mode disabled, give it a location in the one default datacenter. I get to the "Ready to Complete" screen normally - it shows the summary, datastores on the hypervisor, and networks. 

At this point I click Finish, and immediately get:

Operation Failed!

Task name: Add standalone host

Status: Cannot complete login due to an incorrect user name or password.

This happens regardless if I try to add the ESXi host by FQDN or IP address. It happens in Firefox, Safari, Microsoft Edge and Chrome, and I have no ad blockers or content filters installed on the browers I'm trying. I'm using a dedicated machine on the same subnet as the VCSA. 

I am 100% positive that my credentials are correct, and I am using the root user to add the host. I have logged in as root to the host via the console and via SSH with these credentials and have verified them. It only happens with one specific host - I have added others normally with no issue.

What could the problem be? Any insight would be appreciated - thank you.