Merging actors results in meshed up meshes

I want to merge a decent amount of actors in my world into one static mesh. When they aren’t merged, this is what they look like:

And when I merge them, they turn into this:

I’m not sure how to fix this, and why it is happening. I tried both options, combine actors to static mesh and merge actors, but they both had the same result.

I also tried converting it to a BP actor, but that didn’t work either. What can I do?
Thanks!

Are you merging nanite meshes with non-nanite meshes?

Actually, yes. Should I convert all of them to nanite?

Although, I noticed that merging just the main part, the one main mesh with the windows, also results in the messed up windows.

Are the windows using a translucent shader? I would expect that merged meshes would need to be either all nanite or all non-nanite.

Nanite meshes can’t have transparency so that has to be kept seperate.
I think it should be okay to merge a non-nanite opaque mesh with a non-nanite translucent mesh though.

They are all opaque meshes, none of them are translucent. There are so many actors involved in the building, is there anyway to mass-convert them to Nanite?