Second time I’m experiencing this same problem. I woke up this morning to my entire vault being empty without explanation. The only note that is available is the one that was last open/being worked on.
iCloud Drive folder which contained all notes is also empty aside from last file.
I haven’t had issues with iCloud but I also sync to a git repository each time I finish working in Obsidian just to be safe. You may want to explore doing this – it’s pretty easy to do.
Here’s a good example of doing it, although I don’t use the crontab portion of it because I prefer to manually sync each time I’m done.