Images sometimes open up as tiny squares
This doesn't happen all the time, just occasionally, usually when I've got a lot to do and I'm in a hurry.
I open a jpg image up on the screen of my Apple laptop and it appears as a very very tiny thumbnail, perhaps two or three pixels across at the top left of my screen.
So I press Apple 0 to resize it and nothing happens. Then I press Apple + a few times to make it bigger and it increases in size gradually but I still have to manually resize the window.
Then when I can see it as a workable size on my screen it disappears down to the size of a dot if I press Apple 0 again.
The size of the image I am opening is not usually small, I'm talking about normal full frame DSLR images.
I'm using the latest version of Adobe Photoshop CC 2017 for Mac. I've attached a picture to let you see what happens.
I must have pressed something somewhere to cause this or perhaps there is a bug somewhere. Anybody else get it please ?

