Inspite of the site itself is published correct, you got the error:
Unable to connect to Web Presence Builder server. Please contact the server administrator.
[EMERG] [System] /JsonApi/ Base_SyntaxException: PHP Warning : PDOStatement::execute(): MySQL server has gone away file: /var/www/vhosts/4/100809/webspace/siteapps/530/htdocs/include/Zend/Db/Statement/Pdo.php
Timeout defined in the
my.cnf was exceeded.
wait-timeout configuration directive in
/etc/my.cnf and restart MySQL server.