Index changes associated with a previous schema change are still pending. This is because the forest-wide ds-heuristic flag ...

Index changes associated with a previous schema change are still pending.  This is because the forest-wide ds-heuristic flag fDisableAutoIndexingOnSchemaUpdate is set. This flag, when set, disables automatic indexing of existing attributes on schema update.  To ensure optimal performance from this DC, force an index creation by performing a rootDSE attribute modification on schemaUpdateNow and set it to 1.  This behavior can also be turned off by resetting dsHeuristic fDisableAutoIndexingOnSchemaUpdate to 0, then DCs running Windows Server 2012 or later will automatically rebuild indices as they receive this change.