To test if its a HLOD issue, make a new HLOD Layer then in World Settings replace the Default HLOD Layer slots, with the new HLOD Layer.
Don’t build HLODs, just close the Fortnite and relaunch.
If it is there, it is not HLODs
If its not there, then keep using the new HLOD layer and build HLODs
To possibly fix it if its a OneDrive issue.
In UEFN use the Editor Preferences to add a location for your new Fortnite Projects outside of OneDrive, like C:\Fortnite Projects.
Close UEFN
Move the projects from your User/Documents/Fortnite Projects to the new Fortnite Projects folder
Except this project with the issue, Move it somewhere else, so it can’t be found by UEFN.
Open UEFN and download your latest Check-in from URC.
It will go into a clean empty folder.