Several of my co-workers and I have experienced viewports that for some unknown reason become unselectable. Also, if one jumps into model space through the viewport, it disappears completely. I thought I found a workaround in saving the drawing, closing cad, re-launching cad and re-opening the drawing but that doesn't always work. Viewports were all rectangular viewports drawn on layer defpoints. This has only happened on 3 or 4 drawings in the last couple months but I have no logical explanation. Any help would be greatly appreciated.
Thanks.