Sometimes I lose all the data in my scene when I update my blocks. It doesn’t happen always, but I couldn’t discover in which situations it happens yet. A few times I lost my data at work because undo didn’t worked and I had to do all my work again from last save.
I’m using 6.4 and having this issue at least since 6.3. I don’t know if it existed in 6.2 or before.
I recorded a video. Here: https://www.youtube.com/watch?v=L9BzHw5mD3o