Exactly the same issue here for me too. As I said in another post, removing the Volt project attachment fixes the issue, however I’m not saying it’s Volt causing the issues as it could be Blocs, or another program.
I would say it has something to do with the pages/volt being in PHP and preview not working correctly, or something along them lines. So who knows, I’m not an expert.
It only seems to be when you add a new page to a project (I tested on a new project) and add the ‘Volt Blog’ Bric, thats when it seems to go wrong after that, which I guess changes the page to PHP?