Assume that you set up the External Identity Provider, for example, the Forefront Identity Manager (FIM) or Microsoft Identity Manager (MIM) in Microsoft SharePoint 2013. Then you install the Forefront Identity Manager Connector for Microsoft SharePoint User Profile Store on the FIM or MIM server. In this situation, after you set up the sync, the membership changes that are queued in ImportExportStagedMember.ImportExport_PostImportMembers aren't called. The memberships also aren't synced.
To fix this issue, install the February 7, 2017, update (KB3161988) for SharePoint 2013.