Okay so it seems that this happens because your project is somehow corrupted. Try to load a backup of your project and it should fix the issue. I got it fixed like that. So basically what this method does is to load an earlier step in your project which was working fine. Just remember to delete the everything associated with the old project and voila it should work.
If you’re too afraid to just completely delete it, just change it’s location so that Unreal Engine can’t find a way to bring anything from there inside the backup project.