PNG files suddenly not visible in Photoshop (macOS)

.png files are very useful to me having visible layer with transparent background and have worked beautifully for years, but now, suddenly, without apparent reason, the contents of the file are not visible and also not visible when I try to bring the layer over to a file I am working on. My first thought is I must have hit some keystroke that makes a layer not visible but that makes no sense to me. I need help on this as this is very important to my workflow and is now not working. See example screen shot showing .png open and in front of an image I was working on - showing window with nothing to see but I know there is a visible layer, or at least was visible just yesterday.

TIA,

Ken

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