Shadows are flickering / disappearing / acting weird
Occlusion culling is currently not considering shadow casters and incorrectly culls them along with everything else outside the camera’s viewport. The workaround is to disable dynamic shadows.
Generated assets have way more vertices / triangles compared to original scene
Either the detail level is too high (lower your "Smallest Feature" parameter) or the scene was very low detail to begin with. Umbra has some overhead that may become an issue if the scene detail is very low. See the section on good and bad scenes for more information.
Generated assets are shaded differently compared to original scene
Current material support is very limited (see the material section) and may result in shading differences between the original and the materials generated by Umbra. Support for user defined materials is planned. There might also be some differences due to lack of proper support for Unity’s global illumination (see lighting section).
Generated assets sometimes disappear near screen edges
Missing (typically very jagged) geometry on screen edges is a known bug with the interaction between LOD generation and occlusion culling. There is currently no workaround.
I experience stuttering when moving around the scene with generated assets
The main performance bottleneck is currently texture upload. Due to Unity limitations this happens in the main thread and may take some time for large textures. Fixes for this are planned. The easiest workaround is to use larger values for smallest feature.