I updated yesterday to Wordpress 5.0 and wanted to test the new editor. Unfortunately it didn't work like the beta (Gutenberg)-version before. After opening a github-issue and more googling today, I found the solution. The culprit was nginx and that it doesn't work with the REST-API from Wordpress with the configuration as it was documented in the past. Thus I had to change it and Stack Overflow saved the day again.

Here is what I did:

Change:

       location / {
        try_files $uri $uri/ /index.php;
        }

to

       location / {
        try_files $uri $uri/ /index.php$is_args$args;
        }

and add

   location ~ ^/wp-json/ {
    # if permalinks not enabled
    rewrite ^/wp-json/(.*?)$ /?rest_route=/$1 last;
}

So now I have only to find a way that h-cards work with twenty nineteen…