If anyone else has encountered the bug indicated in the title of this discussion, we found adding the following SRV records in our DNS for each of our AD DCs significantly improved the responsiveness of ADUC, if it did not resolve the issue entirely.
_ldap._tcp.default-first-site-name._sites.<dc fqdn>
_ldap._tcp.<dc fqdn>
Each one of those should then point to the priority, weight, ldap port, and fqdn of the named DC, similar to how you already likely have setup for your other domain _ldap._tcp SRV records.
Also, for us, ADUC takes anywhere from five to 10 minutes to open with this problem.
