Here are a few more things to try.
- Make sure your project folder is not managed by OneDrive. Source
- Restart your PC and launch EGL/UEFN as admin. Source
- Leave your team and rejoin it. Source
- Convert your map to and back from an IP. Source
- Start a Session from a different project. You may need to delete C:\Users\\AppData\Local\UnrealEditorFortnite. Source Source
- Select everything in the Outliner, right click, and run Save Selected Actors. Source