Corner handles not showing with direct selection tool

Hello,

I have this off and on issue with illustrator not showing corner handles in all instances, I'm aware of the need for closed paths and also to reset with the anchor tool. The corner adjustment appears if I hold option - switching back to black selection tool. But then they dissapear again when released, same for manually toggling. 

So I assume based on that it works with one not the other, that the path is suitable for them (closed, etc).
For context, my need for this is to be able to adjust just two of the four points, for instance, on a square.

Appreciate any help.