https://bugs.openldap.org/show_bug.cgi?id=9858
--- Comment #3 from Howard Chu hyc@openldap.org --- Looks like syncrepl caused the particular backend's config to change, forcing it to be closed and reopened. One of the changes affected index definitions, so the online indexer task was added to the runqueue. But because of the close and reopen it was running on a backend that was no longer open.