Ran a Gaussian blur filter on a single layer. When the filter completed the file was completely jacked - random holes missing from multiple masks and layers and preview totally scrambled. Tried undoing, going back in history and there was no going back. So I saved the file as a copy in a different location to see if the messed up layers were permanent. Closed photoshop and restarted, opened the file and yes, the layers were indeed permanently ruined, holes cut out in random places.Went to open the original file which had been saved a few minutes before the photoshop error had happened and that file wouldn't open, Error said something like "this file is not compatible with this version of photoshop". Tried opening from another station that uses CS6 rather than the cloud, same error.
Was able to alt-drag the original file to make a copy and that file opened and was not ruined... thank god! Also, about 12 hours later was able to open the original file that was throwing the error message no problem, weird.
Possible hardware failure? Seems like the kind of thing that might happen with a RAM error, though to be fair I've seen reports here on the forum of people running Macs getting corrupted files after doing Gaussian Blur for years.
But a software failure wouldn't explain why you couldn't open a file, then you could later. That really sounds like an intermittent hardware issue. Have you done diagnostics on your system lately?
P.S., RAM errors do happen. The possibility of RAM error is why quite a long time ago I started only buying systems with ECC (error correcting) memory. If there's a failure too complex to correct it will stop the system and tell you where it is. I find that a FAR more preferable option than intermittency.