Something I just noticed is that the option to unhide a selected element isn't shown unless you use Reveal Hidden Elements first. I went into a 3D view to select elements to hide in an elevation and did the same thing to unhide an element I accidentally selected along with the others but the option wasn't there until I turned on Reveal Hidden Elements. I then had to go back to my 3D view to select the element again as it was behind other elements. The option to hide an element should become unhide if the element is already hidden.