Large blank squares randomly appeared, and ruined, photoshop file

Hi guys,

I was working on a large layered file last night and all of a sudden large-ish blank squares appeared within the whole file, on different layers, it wasn't just a white or black square like sometimes comes and goes when you zoom (a known issue), but this time it was like it literally deleted the area it covered. 

I had noticed this earlier in the day, but at that time the blank square was only on one layer and went away as I continued to edit, so I didn't think much of it. This time it affected so many layers and wouldn't go away at all.

I tried everything to fix it, (even if I stepped-back in undos it was still there so I don't think it had anything to do with my own editing).

I did a bunch of googling as well and have already tried many possible tricks/tips in regards to the graphic processing options etc etc, I can't tell you how many times I altered photoshop options then restarted the app/my computer, nothing changed.

If I duplicated the file the blank squares were then saved into the copy, unlike the original, if I tried to remove a layer and drag it onto a whole new canvas the empty square area went along with it, the whole file was basically corrupt (I lost days worth of work despite saving every 15mins, the blank square just wouldn't go away ruining all files involved).

I sadly can't post any screenshots as the file it happened to is confidential for a client, but hopefully my description is clear enough to understand~

I have the latest photoshop, with all latest iMac updates etc, I even tried opening the file into an older version of photoshop but it wouldn't go away. Oddly enough though if I viewed just the thumbnail preview image of the file in finder no blank squares appeared, so was pretty confusing.

Any advice is grateful, I'm pretty worried it's going to happen again on future documents, def. can't afford to lose so much work so instantly despite doing the right thing and saving so often. 

Thanks!