The expected & previous toolbox behaviour when a Sky object is inserted from the toolbox is for it to remove the previous skybox(es), but the current behaviour doesn’t remove the previous ones which results in only the most recently inserted skybox being visible, which is confusing behaviour and results in the developer having to delete skyboxes frequently if they’re trying them out.
This happens 100% of the time on any place and has since the introduction of the Lua toolbox in late 2018.
That might be intended behavior. I mean, why would you want existing skyboxes deleted? What if you had a custom skybox your Team Create buddy accidentally replaces from experimenting with new skyboxes?
You’d be upset about your custom work being deleted by accident.