In the Level Editor's "File" menu, there is a "Favorite Levels" list, which is persisted in the config file "EditorPerProjectUserSettings.ini" under section "[FavoriteFiles]".
Manually editing this list in the config file does work correctly, but adding and removing levels from this list using the Editor's UI does not. The Editor updates the config file correctly at first, but when opening a new asset editor (e.g. a blueprint, a material, a different level...), the list is reverted back to its previous state (effectively disappearing if not previously edited manually in the config file). The list is also reverted when closing the Editor, which keeps any changes from persisting at all.
Mentioned in the bug report by a user: the cause of the issue seems to be that the class FMainMRUFavoritesList is used by both FMainFrameModule and UAssetEditorSubsystem. And, in its current implementation, the favorites list always reads and writes from two config sections, the overridable "MRU" section and the hardcoded "FavoriteFiles" section. The favorite levels are known by the instace inside FMainFrameModule, but not by the instance inside UAssetEditorSubsystem (which maybe should contain a list of favorite assets, or no favorite list at all). As a result, these two classes write conflicting versions of the "FavoriteFiles" section to the config file.
Steps from the user:
1. Create and open a new level
2. File - Favorite Levels - Add Map to Favorites
3. Optional: Check EditorPerProjectUserSettings.ini [FavoriteFiles] section - the map was added there
4. Open any asset editor (any BP will do)
5. Optional: Check EditorPerProjectUserSettings.ini [FavoriteFiles] section - the map was removed (or the whole ini section if no previous fav maps were present)
6. Close and reopen the editor to find that your favourite list is not what it was in the previous session
Notes from the reporter:
I) Steps 1-2-6 are enough to reproduce the bug
II) Step 4 can also be replaced by opening a different level and clicking the "File" menu
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-200874 in the post.