Unfinished index builds are not restarted in standalone mode. When the server is started with --recoverFromOplogAsStandalone, a commitIndexBuild oplog entry during oplog recovery is a no-op for these unfinished indexes. This has the potential to hang oplog recovery when replaying oplog entries after the commitIndexBuild oplog entry, like renameCollection with dropTarget=true which checks that there are no index builds in progress.