I’ve found a solution for this that fixed it for me. in my project in 4.2 i had disabled (unchecked) “update navigation automatically” in Editor Preferences as it was taking to long to place meshes. since i updated to project 4.3 i could not enable it as Editor Preferences in menu had disappeared. i work on a mac and found Editor Preferences has moved to Apple tool bar. so enabling “update navigation automatically” has got me working again although you’d think Build at runtime settings should have worked anyway.
hope this helps, let me know.