I am using Gutenberg on a couple of WP.com sites. It is working OK on the site that is built on the Independent Pubisher 2 theme but it is creating problems on this site at Photographworks.me where I am using Rosalie theme.
The text comes out super-small and some images simply do not appear at all.
I have found that one clunky way to make the text normal size is to expressly change it to a wrong size such as XL and back to M.
Watch this space for updates.