Sorry to hear it's happening to others. Still no idea how or why it happened to me in LA. I've been saving my own session file backups, renaming them and .zipping them to hopefully "contain" functional files.
Can you describe how and what happened for you? For anyone else, are you all using MacOS? I am on 10.12.6
In my case, it happened once in the middle of a job being open. I looked up and out of nowhere audio and video were gone.
In the second case, it happened when I returned to a session the next day. I had worked with no issues all day until 5pm. Came back to see that my 5pm file was corrupted and all others past until 1pm when I started were bunk.
Avid has been able to help me yet, other than this thread, which is inaccessible, aside from caching text in a google search for "pro tools project files missing"
http://duc.avid.com/showthread.php?t=401217