If you tell me which (Browser, PC download, or Mobile) you are using to play the patched version, I can give you specific troubleshooting steps for that version.
The developers released the 1.4.2 hotfix specifically to target rendering pipeline errors. The "Blackout" wasn't just a lighting bug; it was a failure of the UI layer to handshake with the 3D engine after long play sessions. Key Patch Highlights dawn of the dead blackout patched
While the specific "Blackout" game received a patch, the terms are often used in related zombie gaming contexts: Everett Blackout Dawn of the Dead If you tell me which (Browser, PC download,