I am so glad I found this thread because I am having the same issue. I just deleted my previous message about it on accident, lol.
Anyway, it happens to me in both V6 and V7 for Mac, both are updated to the latest builds and my computer is running MacOS Catalina 10.15.7 (19H524)
It seems to happen if I click one too many times right after exiting the block editor - all of a sudden everything disappears. It’s not hidden or deleted, and I cannot undo the action to get it back, like others who have posted, I have to revert to a previous version to fix it.
Please let me know what I can do to help with this - I copied the model that appears to be “blank” and could share that with the McNeel team to take a look… The file is still 17MB even though it looks like there is nothing inside.
I can send more info on my computer etc as well if that’s helpful. Let me know.