title: phpmyadmin failed to start due to Symfony/Polyfill errors
body: <p>I opened PMA and I got this error:<br />
  <strong>No such file or directory in /usr/share/php/Symfony/Component/Cache/autoload.php on line 6</strong></p>
  <p>I solved downgrading <strong>php-symfony-polyfill-apcu</strong> back to <code>1.6.0-2</code> (as I saw in another topic).<br />
  Although I got another error:</p>
  <p><strong>Fatal error: require_once(): Failed opening required 'Symfony/Polyfill/Mbstring/autoload.php' (include_path='.:/usr/share/php') in /usr/share/php/Symfony/Component/Console/autoload.php on line 3</strong></p>
  <p>I can't figure it out.
  I'm on <strong>ubuntu 18.04</strong>, I use <strong>apache</strong> (running and working).<br />
  Hope somebody can help me. Thanks!</p>