The message is also displayed when using latest version (i.e: upstream main branch). It is indeed a minor regression of a recent change. (Issue 5598 - In 2.x, SRCH throughput drops by 10% because of handling of referral (#5604)) The root cause is that during backend initialization, a subtree search is now performed on the backend to determine if the subtree contains smart referrals or not. But when starting the parent backend, the subsuffix backend is not yet started and the search fails. The impact is quite mild: If the db contains smart referrals, there is no impacts. In the other case, the optimization that prevent the performance drop is disabled until next occurrence of the internal search (which by default happens 5 minutes later) In other words: There may be a 10% performance drop for the 5 first minutes after the startup.