Every so often I get an error that causes the selection box to become invisible (not good for a selection box). In the attached picture, the mouse cursor wasn't captured in the screen grab but it's hovering over the margin corner and it has a check mark next to it. You can see the pet pallet has adjust polygon line icon is active but the selection box for it isn't visible. When this happens, I have to save and restart Archicad in order to fix it.
I'm not sure what causes it. I've never noticed a pattern. I can relate what happened this time and maybe that will provide a clue.
I was adding a "save and place view on layout" view to a layout but accidentally placed it on the wrong layout. I cut and pasted the view to the right layout but as I tried to paste the layout started to update the views and Archicad gave me the busy chime. I waited until it was done, pasted, and when it placed the view the selection box was invisible.