Just a quick post on how this issue was investigated and subsequently resolved. The root cause in your situation may differ from mine.
When signing onto the web console with Active Directory credential, the admin receives the error below:
The first step is to confirm access to the web console with the local administrator account. This account is created during the initial setup of VMware Workspace ONE UEM. Then, navigate to GROUPS & SETTINGS -> All Settings -> System -> Enterprise Integration -> Directory Services. Then click on TEST CONNECTION at the bottom of the page.
This error message is pretty self-explanatory. Given that we had successful AD authentication in the past, the next step is to determine what change, if any, was related to LDAP. As it turned out, we recently required communication with the read-only directory server on TCP port 636 (secure LDAP or LDAPS). The cloud connector server, however, didn’t have the necessary firewall rule to communicate to the directory server on port 636 (i.e. quick verification through Telnet.)
Once the firewall rule was created, the admin was able to log in again with AD credentials.