This happens to me too. I have the Designer on W10. It's always done that, just randomly, the selection box and handles all disappear. I can still move/rotate/resize/etc objects as if the handles were there but it's pretty hard without actually being able to see them. Only way I've found so far to bring them back is to restart the program.
I haven't yet figured out exactly what triggers it to disappear but it seems like when I do a lot of moving, copying, duplicating, things like that, it tends to happen more.. I don't know. Could be that my 5yo laptop just can't keep up?