Different plane (the hi-res plane) and the texture didn't interrupt on the face. However, it looked completely different. Same settings, same shader, different plane (looks like poo):

Seems like the texture kinda repeats on the way down. So, might it be a mapping issue? Since the high-res square has more polygons and might be mapped differently? No idea.

I'll make my own square next, in Blender, UV-map an image to it, and see if I can attach the shader. But first, I'll have a go at your suggestions next, Bill and see how I go. BTW, you can see that artefact in my hair example above.

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks