Does Project Zomboid 42.21 Fix Disappearing Zombies?
Project Zomboid 42.21 Unstable repairs disappearing zombies in solo and multiplayer. Back up 42.20.4 saves before testing the update.
Project Zomboid 42.21 Unstable fixes zombies disappearing when players leave and return to map chunks, according to The Indie Stone's September 23 release post. The correction applies to single-player and multiplayer, with multiplayer zombie duplication also addressed.
The studio expects existing 42.20.4 saves to work, but explicitly asks players to back them up first. Keep that backup before opening the save in the new build.
Choose Unstable to try 42.21
On Steam, open Properties, then Game Versions & Betas, and select Unstable. This release has not moved to the Stable branch.
The update also improves visibility around very large trees and vehicles, and fixes some vehicle-coordinate problems under high latency.
The Indie Stone gives no date for promoting Build 42 to Stable; that decision depends on feedback. If the disappearing-zombie bug is why you return to testing, confirm 42.21 before checking the affected area again.