Don't know what is causing this, but it has gotten worse over time (many months), and seems to change its "symptoms" evry now and then.
I am running an Apple iMac 2020 5K retina, 3.8GHz 8-core i7, with 128 GB memory. This machine has a AMD Radeon Pro 5700 XT 16 GB. OS Montery 12.4.
Most recent problem occured yesterday, when after zooming into a document, some kind of wierd effect happened, where parts of the background image was duplicated, and scattered across the document in a semi-random pattern (squares starting about in the middle of the document and continuing to the right and down. The only "normal" part of the background image that remained was now only about 1/4 of the image size in the upper left corner. All the "square" duplicates looked like they were overlaid over themselves with different blends and/or specific color channels, so that these squares, for lack of a better description, looked like Andy Warhols' Marilyn Monroe painting, where it was the same image, but with different color combinations for each one. Some had truncated-file looks with video noise lines in different spots. I could change the colors and noise/defects by turning the visibility on and off for the upper layer. I could have probably continued to work on it, but nothing I did would make the background defects go away. I saved the files as a different version, quit Photshop and reopened it. The saved file now had all the areas covered by the duplicated errors as mising and just black. The only part of the original image that remained was the upper left corner. The upper layer was intact.
This kind of "video" effect has presented itself before, sometimes as a "golden ratio-like" pattern where the duplicated image was presented as progressively smaller and smaller and in different areas. But this was the first file I had to save.
Auto save is turned off. 84 GB memory is assigned. Use Graphics Processor is checked on. Have 455 GB free scratch disk space. I usually have several apps running at the same time, InDesign, Illustrator, Acrobat, Mail, Firefox, Linotype Font Explorer... Illustrator also has funky visual problems with screen redraws at different zoom percentages. Annoying, but does not affect the file.
Still glitching now with Disable Native Canvas checked. Screen freezes when zoomed in, and nothing will get the image to scale back out. All other open files can be scaled fine during this glitch. Can select different scaling sizes but image will not move or scale down even if the scaling states it is at 100% or less.