This was mentioned in the latest stream by the way: https://youtu.be/G6RO6mNBX40?t=44m12s
Had it myself plenty times, but it happens most commonly when switching between snapshots, especially with a lot of items. It could've been that it happened on your last load and didn't notice for some months later, that happened to me. On my nearly 10k item build, it happened and I didn't realise, like my last 20 manual backups for it were corrupted, luckily I found one single random save of it that worked with only about 300 items missing.. Was so relieved..
What I do now is well first, I don't use Steam cloud because I don't like the idea of automatically uploading possible corruptions.
I don't use snapshots to load condos, I go out the game and manually copy the files in. I tested a while ago my condos 1 by 1 and if they loaded I copied them to another folder as my "stable" files. Whenever I want to load one, I copy it in and load straight into it, this worked fine for me now for a good while, bit of hassle but no corruptions since and my files are secure since I know each of them will load fine.