A single savefile is not appearing in-game anymore

A save-file where I had over 600 hours clocked in has stopped appearing in my list of saves in-game despite the files still (I think) being there.

OS: Windows 10.

Game version: latest.

Packs: Most expansion packs and a couple of game packs.

CC: yes, plenty, including .ts4script-files.

Time problem occurred: Not sure, but I was playing another household and then went back to play my main one only to find it gone. Possibly after the latest update.

Thing to note: I had my game syncronised over dropbox to another desktop, and the savefile in question has never appeared on that one but now it doesn't appear on either of my computers.

My backup files didn't work either leaving me to think that it is the game itself that is at fault.

All my other saves work completely fine.

I have tried following this and this guide to no avail.

I have located two sets of save files that sends me only to the big play-button on the main screen leaving me to believe that these are my non-working files.

A much older in-game copy of the save in question works just fine.