I saw this post:
https://theme.co/apex/forum/t/cornerstone-isnt-working-after-the-update-to-3-3/44963/10-3-3/44963/10
and I just wanted to say that before I updated just now, I was able to edit a page containing classic columns, but now I can’t see them in Cornerstone. Fortunately, I updated on a test site first because I’ve been burned before, so I’m not in a panic, but I wanted to let you know that this is also happening for me.
I’m attaching 2 screenshots. The first one is after the update and the second one is before. (And yes, I cleared the cache.) The test site was a fresh clone of the live site.