Failed to generate Nanite data for mesh with bDoFastBuild enabled

If "bDoFastBuild" is enabled on a Static Mesh asset, in-editor it will never be able to have Nanite data built for it, preventing the Static Mesh from using Nanite.

There is no way to fix this issue for that asset, as "bDoFastBuild" cannot be disabled without custom C++ code.

This member is also not visible in the editor, leading to confusion as to why a Static Mesh asset is unable to use Nanite, despite having "Enable Nanite Support" checked.

These reproduction steps use the blueprint-callable function "UStaticMesh::BuildFromStaticMeshDescriptions(..., bFastBuild = true)" to enable "bDoFastBuild" in-editor. Any other method, intentionally or by coincidence, that enables "bDoFastBuild" in-editor will have the same effect.

Also tested on //UE5/Release-5.6, CL 45232827

1. Download the attached test project and open
2. Duplicate the static mesh "SM_Cube_COPYME", and save the duplicate. The following steps will permanently change the duplicate asset, so don't use SM_Cube_COPYME directly, in case you want to repeat the steps.
3. Select the actor "BP_Mesh_Breaker"
4. Add the duplicated mesh to the field "Mesh To Break" in the details panel, then click the button "BreakMesh"
5. Save the duplicated mesh
6. Enable Nanite on the duplicated mesh.
7. Observe that no Nanite data is generated, no Nanite stats are used, and it does not render using Nanite, despite having the "Enable Nanite Support" checkbox enabled