Cannot select or delete viewport. Problem solved?
I had a case with rogue vport. It was on top of another identical in place and size. Three in the layout, actually, two visible and workable, one not. I turned all layers on, thawed all layers, checked layout freeze/thaw statuses, and so on. Nothing. I did a search and found many people with similar issues. Read about clipping and re-clipping, QSELECT, etc., and none of that worked for me.
Started playing with some buttons on the bottom tray. Selected "Maximize Viewport" (you must be in the vport to do this), re-clicked the same button to minimize, and the boundary popped up and stayed there. (It was on the same layer as the other vports, btw.) I was then able to select the vport and delete it.
I won't claim this will work for everybody, but am posting this as something to try should somebody do a search sometime in the future.
We were having the exact same problem in my office laast week.... I will pass on. Thanks!