Hello @ejoweb,
Ivan Atanasov from SiteGround here.
If you update a post, this action will trigger a hook defined in class-sg-cachepress-supercacher.php that is meant to purge the cache automatically:
191 add_action( 'save_post', array( $this,'hook_add_post' ) );
192 add_action( 'edit_post', array( $this,'hook_add_post' ) );
Additionally, SG Optimizer will skip cached content for users that are logged in the application dashboard. Meaning, if you are logged in your WordPress Dashboard, you should not be presented with cached content.
Editing a post with Gutenberg should not be an exception. If is possible that this is a result from several caching mechanisms working at the same time.
I would recommend posting a Support Ticket from your SiteGround User Area so that this can be reproduced.