
A 502 bad gateway WordPress error is a proxy reporting that the process behind it died, vanished or sent a broken answer. Find out who sent it, then read the log line: a PHP fatal error is a 500, and a slow request is a 504.
Maximum execution time errors mean PHP stopped a script at its time limit. The number in the message tells you who set that limit: 30 is usually PHP or your host, while 300 or 600 means WordPress raised it.

The missing the MySQL extension message means PHP cannot find the function mysqli_connect, so WordPress stopped before it touched your database. Check the PHP version and the extension list for the account, choose one MySQL driver set, and reload. Plugins, themes and wp-config.php are not the cause.
