Inter-Site Topology Generator Invalid
ISTG has invalid on all Domain Controller on the network after you demote a DC and trasfer roles and then rebuild it.
If demoted Domain Controller is the first DC in site - If yes then this DC holds the role - ISTG Server.
Initially the first server in the site becomes the ISTG owner and this this role is communicated by normal AD replication.
Moreover, this role is not changed automatically. Server holding ISTG role notifies other domain controllers about its presence by writing the *InterSiteTopologyGenerator* attribute in Configuration Naming Context at a specified interval.
Another fact is that another DC as an ISTG server doesn't take over unless it knows that DC hold ISTG server has failed.
To correct this issue:
You can edit the following registry value to modify this behaviour:
Value Name: KCC site generator renewal interval (minutes)
Value Data: Number of minutes between updates to Active Directory
Value Name: KCC site generator fail-over (minutes)
Value Data: Time that must elapse before a new ISTG is selected, in minutes.