I ran into this problem. Very frustrating. I had to delete all the foliage in order to solve this “light needs to be rebuild” issue. I did not need to delete other maps or restart the map again.
My Project is an open outdoor mall and it has a huge world. Highway, entrance, parking and 40 warehouses. Very extended.
I am using stationary lights (both directional and skylight are stationary).
I left some trees tough, but they were placed as mesh in the scene and not as foliage.
I fear if I redo the foliage again, I will run into the same problem.
Any suggestions please?
Is it a good idea to set the foliage as “movable” and enable modulated shadows in the directional light?