How to Fix (Slow/Stuck) Download of Fortnite Game from the Epic Games launcher

This issue is sometimes caused by your router struggling with the number of connections due to too many downloads happening simultaneously. To work around this issue, try the following steps. As a note, this workaround may result in lower download speeds but should allow your download to complete eventually.

• Navigate to the following location

• For Windows: Computer> Local Disc (C:)> Users> [your username]> AppData> Local> EpicGamesLauncher> Saved> Config> Windows.
• Note: The AppData folder is hidden by default. If you are unable to see it, you will need to change your settings so that you can. To do so:
• In Windows Explorer, click Organize
• Select Folder and search options
• In the View tab, under Hidden files and folders, select Show hidden files, folders, and drives
• Click Apply

• For Mac: ~/Library/Preferences/Unreal Engine/EpicGamesLauncher/Mac

• This directory is sometimes hidden. To find it, from the top bar, select Go> Go to Folder and paste the above path in the text box

• Open the file named Engine.
• Add the following lines to the end of the file:

1. [Portal.BuildPatch]
2. ChunkDownloads=3

• Save the file.
• Restart the launcher
• Retry the download.

SOURCE