images not displaying in photoshop- can on ly see a small ribbon at the top of the screen.

[DavidLaufer]

Photoshop is driving me nuts- just within the last 4 months, if I open a file, PS shows only a small ribbon of the file at the top.  (attached example 1) I can fill the screen by zooming in, but then when I hit Command-zero to fill the screen it returns to only displaying the small ribbon. sometimes ribbon is repeated at bottom of screen (attached example 2). Problem is inconsistent- some files open OK, others don't display. If I zoom in, it displays a detail with a black bar then repeats the same ribbon of the image at the bottom. Hand tool does not allow me to move the file. Is this a program error, or do I have some setting wrong? arrgh

[DavidLaufer]

Sorry I should have added to the original post I am on a 2020 Macbook Pro, running Big Sur 11.2.3, and the latest builds of Photoshop.