Not sure if that is the issue, but I can see that models are loading async in the background while the camera is orbiting the scene (preload set to false). Which makes sense to provide fast loading times. Though that means also that the models aren’t in place to be rendered when the light mapper runs.
Could you try setting them just for a test to have preloading enabled?
If that is the issue, I’d imagine a solution is to run the lightmapper at a later point when all models have loaded and are in place. There is a number of posts on how to do that on the forum.
EDIT: I missed that you said your issue is in the editor and not on runtime, I will let you know if I find something on that.