I can’t seem to work it out:
If I create a spline with a StaticMesh and an Emissive Material, enable “Use Emissive for Static Lighting”, it just does not work.
If I do the same with a simple cube it works. So this seems to be related to the spline.
For everyone having the same problem:
I just solved it myself, I had to set every Component to Static, not only the AddSplineMeshComponent (eg the spline itself, the scene I have it capsuled in…)