Troubleshooting

Plugin does not load

In Epic Games Launcher > Unreal Engine > Library, confirm Spectral is installed to the engine version used by the project. Acquiring it on Fab is not the same as completing Install to Engine. Then enable Spectral in Edit > Plugins and restart.

Refresh Fab Library if it is missing and confirm the launcher uses the account that acquired it. If you previously installed manually, check for a duplicate project-level copy before using the Fab-installed engine copy. Follow Installation; normal Fab setup does not require extracting files or building the plugin yourself.

Bake is blocked

Read the first prerequisite error before changing bake quality.

Message or condition	Check
Lighting baking is not supported on Vulkan	Restart the Windows editor with -dx12, use the required bake configuration, bake and save, then restart on Vulkan for playback
Hardware ray tracing unavailable	Enable required settings, use DX12 and SM6 on Windows, restart
Static lighting disabled	Enable Allow Static Lighting and restart
Conflicting baker	Disable the separate GPU Lightmass plugin
No stationary shadow channel	Reduce overlapping stationary lights or change appropriate mobility
No enabled static or stationary lights	Check light mobility, visibility, and enabled state
Ray tracing still unavailable	Check plugins that can disable it, including RenderDoc integration

noteNote

The preflight is designed to block unsupported setup before starting the bake. It does not fix every rendering prerequisite automatically.

Shader compilation fails after an update

Check the engine version and installed Spectral package. Use Update Shader Hooks, restart, and allow compilation to finish.

If the hook operation reports a file-access or unsupported-source error, resolve that specific problem. Do not overwrite engine shaders with files from another version.

Project settings do not stay changed

Check whether project configuration files are read-only or need checkout. Fix Settings writes DefaultEngine.ini. Restart after renderer changes and save modified levels.

Visualization preferences, Fog Quality, and Save level settings as default use Config/DefaultGame.ini. Tonemappers are saved with the level, not by saving that configuration file.

Import or level defaults do not do what I expected

Stop Play and lighting or reflection baking. Select a different saved source map before importing, then save the destination. Import copies the included Spectral level settings, not actors, baked lighting, PCSS configuration, fog quality, or visualization preferences.

Saving defaults affects unconfigured levels in this project. It does not overwrite an already configured map. Use Import for that map instead. See Level settings and defaults for the exact scope.

Probe markers are missing

Check Visualize > Visualize Global Probes, the selected volume's local display, and marker scale. Temporarily disable Hide Intersecting Probes: it can hide all red intersection markers in a region without removing its baked data. Auto Disable Visualization When Baked also turns off the local display after baking. Display preferences are separate from whether probe lighting is enabled.

Probe lighting is missing or stale

Check that the volume is enabled, covers the object, and reports Baked rather than Not Baked or Rebake Needed.

Inspect the probes with Visualize Global Probes. Duplicated volumes and incompatible old data need another bake. Moving a light does not update captured lighting automatically.

Lightmaps have seams or lost detail

Check UV overlap, padding, the assigned lightmap coordinate channel, and component resolution overrides.

If UVs changed after the last bake, rebake. Compare compression, chart-separated denoising, and seam stitching only after the UV layout and density are correct.

Lighting changes after reopening the map

Confirm the level and lighting build data were saved after the completed bake. Check that the same sublevels are loaded and visible. A cancelled build or a viewport preview is not a saved final result.

For prefabs, check that Capture succeeded and the Blueprint was saved. For reflections, run Bake Reflections after lighting changes. If the data is present but the image looks different, compare exposure, scalability, renderer, and tonemapper settings before rebaking.

The tonemapper selection and each operator's Strength and White Point are now stored in the map. Save after tuning or importing. A different map can intentionally have a different look. A console override can also mask the saved level choice.

GTAO has no effect

Check the rendering path. Spectral GTAO excludes forward rendering, mobile shader platforms, and stereo views. Also check whether the material contains a GTAO Disable node.

Fog is dark or misses emissive lighting

Enable Use Probe Fog Lighting and check probe coverage. Inspect the separate contribution multipliers.

Older data may not include the emissive contribution. Rebuild lighting rather than increasing a multiplier on missing data.

Fog Filtering has no visible effect

Confirm volumetric fog is visible and current shader hooks are installed. Compare Trilinear against a higher-quality option from the Fog Filtering dropdown. Before UE 5.8.3, the menu has only Trilinear and Spectral's custom Bicubic; native Bicubic and Tricubic require the newer engine support. This filters the rendered fog grid, not the baked probe field; Features > Probes > Interpolation is a different control. Compare a coarse grid's cell transitions from the same camera. A fine grid may already look smooth, and filtering cannot recover missing probe lighting, add depth slices, or remove temporal trails.

Capsule lighting does not change

Confirm that native capsule shadows already work, the object has valid capsule data, and it is inside baked probe coverage. Enable the separate probe capsule lighting switch.

Prefab lighting is outdated

Rebake the source instance and capture again after geometry or lighting edits. Capture refreshes loaded instances automatically. For construction-script changes that replace components, the Blueprint-callable Apply Lighting function can reapply the stored payload. See Lightmapped Prefab.

Information to include in a report

Send reports through Contact.

Include:

• Spectral and Unreal Engine versions.
• GPU, graphics API, shader model, and rendering path.
• Shader hook status and the first relevant error.
• Steps to reproduce, including whether the issue occurs in a small test level.
• Screenshots of the affected controls and result.