hi @USE_CODE_NHZ ,
From the bit of log you sent looks like your UEFN is corrupted, because you have source code lines numbers for the Windows Visual Studio.
The first thing to check is UEFN and Fortnite are not corrupted.
Restart the PC, and then verify as in the link below.
See if the Anti Virus check has flagged wrongly part of UEFN as malware
Another post in this thread shows how to Exclude Fortnite programs from Windows Defender
Exclude Fortnite programs being wrongly detected virus
The Fortnite Content server is refusing/objecting to the UEFN compressed code.
If you are still getting an error you may have to uninstall Fortnite/UEFN