When altering "Coordinate Light Map Index" in a static mesh when "Generate Lightmap UVs" is enabled in LOD 0 the engine will crash or "Coordinate Light Map Index" will be set to 0.
A demonstration can been seen [Link Removed].
Found in 4.24.1 CL#10757647
Reproduced in 4.25 Main CL#10872318
1. Make a copy of the Cube mesh in the content browser.
2. Open the copied cube static Mesh.
3. Disable, then re-enable "Generate Lightmap UVs" in LOD 0.
4. In LOD Settings change "Number of LODs" to a number greater than 1 and select "Apply Changes".
5. Attempt to set "Light Map Coordinate Index" to a number greater than 1. IMPORTANT: You need to submit the change using the Enter key, simply changing focus won't reproduce the bug.
Result: Light Map Coordinate Index will be set to 0 or the engine will crash.
Expected: Light Map Coordinate Index will be set to 1.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-86187 in the post.