Issue Overview

Wordpress 4.9.4, PHP 7.0.19, Database Percona 5.6.35
Publish or update a post doesn't work ("Updating failed") with Gutenberg 2.3 and 2.4.
Deactivating all other plugins does not help.
Changing language from German to English does not help.
Deleting Gutenberg, logout from wordpress, login again , reinstalling Gutenberg does not help.
Tried with Firefox, Chrome, Opera - does not help.
Only if I make a rollback of the plugin to version 2.2 everything works again.