I had this problem where building the light would never succeed, I would always get the “lighting needs to be rebuilt” message. I found a solution and post this as answer so that I can close this question immediately.
In my case I have an open world setup and tried to build one level at a time. Whenever I would play though and levels were loaded that I built previously I would get the message that lighting needs to be rebuilt. Console command “DumpUnbuiltLightInteractions” would then list all my assets in the levels.
Well to make it short, after investigating I found out that the problem is either a bug in the engine or it is a planed behavior that is not documented.
It turns out the following scenario will trigger the eternal rebuild request:
Create an actor BP. Name it “A”
Put a point light (or any other) component into the BP and make it stationary
Create a second actor BP, name it “B”
Put a child actor component into actor B and assign blueprint A to it
Create a test world
Place actor B in the world
Rebuild light
Play
This will trigger the message. The key is to NOT have a child BP which in turn contains a light component. UE is obviously incapable of creating the correct light setting in the world. Instead you will have to add the light component to BP “B” directly, then lighting build will work
If you believe this might be a bug then please consider reporting it using the new and more structured Bug Submission Form which is supported by Epic and may get it fixed in future releases for everyone’s benefit. Thanks