This issue is in the operation of World Outliner.
If it attach another actor to the actor, even if you deleted folder that existed before, the folder will exist after restarting the editor.
If it move outside the folder without attaching it, folder can be deleted correctly.

Steps to Reproduce

1. Create a Folder on the World Outliner.
2. Move any Actor on the level to Folder.
3. Attach the actor to another actor.
4. Delete Folder created in Step1.
5. Save PersistentLevel.
6. Restart the Editor.
   When Editor starts up, deleted Folder exists in Step4.

Have Comments or More Details?

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Affects Versions4.174.18
Target Fix4.22
Fix Commit4592835
Main Commit4676940
Release Commit4862694
CreatedJan 7, 2018
ResolvedNov 26, 2018
UpdatedFeb 12, 2019