Check the Engine\Binaries\ThirdParty\Steamworks folder for a steam_emu.ini file. Ensure the DLC IDs are listed there.
Copy all files from that folder and paste them into the main game folder where the executable is located, overwriting existing files.
This is usually a memory or antivirus issue. Re-enable the 2GB RAM limit in the installer and ensure your antivirus is off.
Only download from the official FitGirl Repacks site to ensure file integrity and safety.
Use a "burner" or secondary Steam account to avoid any risk to your primary account.
If your PC has 8GB of RAM or less, check the box that says "Limit installer to 2GB of RAM usage." This prevents the installer from crashing due to memory exhaustion.