Critical Project Corruption in C++ Projects Caused by Enabling/Disabling "Allow Static Lighting" (UE 5.6.0)

Development Rendering
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I am reporting a critical, 100% reproducible bug in Unreal Engine 5.6.0 that leads to permanent project corruption. The bug is triggered by a specific sequence of enabling and then disabling the Allow Static Lighting setting in a C++ project.

The issue first manifests as a permanent loss of dynamic shadows and then escalates to a complete module rebuild failure, rendering the project unusable.

Engine Version: 5.6.0 Project Type: C++

Exact Steps to Reproduce (STR):

The bug occurs following this exact sequence:

  1. Create a new project using the “First Person” template, with the project type set to “C++”.
  2. After the project is created and compiled, observe that by default, the Allow Static Lighting setting in Project Settings -> Engine -> Rendering is disabled.
  3. Action 1 (Breaking Shadows): Enable the Allow Static Lighting checkbox. The editor will prompt for a restart.
  4. After the editor restarts, dynamic shadows from the default Stationary Light will now be permanently broken and will not render on the movable character, even after rebuilding lighting.
  5. Action 2 (Corrupting the Project): Now, navigate back to the same setting and disable the Allow Static Lighting checkbox again, returning it to its original default state.
  6. The editor will prompt for another restart. Close the editor.
  7. Attempt to launch the project again.

Expected Result:

The project should function correctly at all stages. Toggling a core rendering feature should not lead to permanent, unrecoverable issues.

Actual Result:

The project enters a permanently broken state.

  • After Step 4, the dynamic shadows are lost and cannot be recovered, even if lighting is rebuilt.
  • After Step 7, the project fails to launch entirely, displaying an error message: “The following modules are missing or built with a different engine version… Would you like to rebuild them now?”
  • Attempting to rebuild the modules fails.
  • Even after a full manual recovery (deleting Saved, Intermediate, Binaries folders and regenerating Visual Studio project files), the dynamic shadow functionality does not return, proving that the project’s lighting configuration has been permanently corrupted by this process.

Conclusion:

The workflow of enabling, and then later disabling, the Allow Static Lighting feature in a C++ project is fundamentally broken in UE 5.6.0. It causes irreversible damage to the project’s compiled state and lighting behavior. This is a highly critical bug as it can easily be triggered by developers experimenting with rendering settings, leading to catastrophic project failure.

I hope this precise report helps your team to investigate and fix this severe issue.

Thank you.

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I’m not sure about “step 7” , i just tried all the steps and my project launched again normally. About “allow static lighing” checkbox - i don’t think it’s a bug. Epic even updated UI description for 5.6 engine release “When StaticLighting is disabled, it also enables certain effects related to first person rendering, such as player shadows on the ground. " I think it’s just how this new " First Person Rendering” tech is implemented. From 5.6 docs “Limitations and Notes” - " * The second consequence is that Allow Static Lighting needs to be disabled in the project settings. By disabling static lighting for the project, some GBuffer bits are freed up to be used by first person rendering."

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but how can I then bake the lighting while still maintaining the dynamic shadows from the characters?

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(post deleted by author)

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From what i understand this "First Person World Space Representation Shadows” tech doesn’t even work with regular shadow maps (Only VSM, maybe ray-traced shadows too - i can’t test them i don’t have a ray-tracing capable GPU). At lest for me, maybe i missed some setting…
Edit : actually it even says so in 5.6 docs "Without Virtual Shadow Map (or Ray-traced Shadows) there won’t be first person shadows on the ground. "