So I installed a default Wordpress instance. Out of the box, Gutenberg does not save pages/postings, just endlessly says publishing/updating. Logfiles provide no real clue (only something about upstream buffering). Both the issue and the log warnings aren't mentioned in wordpress.org. Activating the classic editor makes the issue disappear immediately. And I thought Gutenberg was meant to make WP easier for people?

@ton sounds like websocket-related issue.