Nextcloud won't run after upgrading Ubuntu Server for ARM devices to 18.04

Nextcloud version (eg, 12.0.2): 13.0.6.1
Operating system and version (eg, Ubuntu 17.04): 18.04.1
Apache or nginx version (eg, Apache 2.4.25): 2.4.29
PHP version (eg, 7.1): 7.2.10

The issue you are facing: Nextcloud won’t start after upgrading my Ubuntu server running on RPi to 18.04. When I enter the server URL in the browser, it does seem to connect but then a file save window pops up and the file name populated there is index.php.

Is this the first time you’ve seen this error? (Y/N): Y

Steps to replicate it: Upgrade Ubuntu Server for ARM devices from 16.04 LTS to 18.04 LTS

The output of your Nextcloud log in Admin > Logging: None, as I’m not able to login.

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

<?php
$CONFIG = array (
  'instanceid' => 'ocbfoy8nwqw6',
  'passwordsalt' => '',
  'secret' => '',
  'trusted_domains' => 
  array (
    0 => '192.168.1.109',
  ),
  'datadirectory' => '/cloud/exthdd',
  'overwrite.cli.url' => 'https://192.168.1.109/nextcloud',
  'dbtype' => 'mysql',
  'version' => '13.0.6.1',
  'dbname' => 'nextcloud',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => 'nextclouduser',
  'dbpassword' => '',
  'installed' => true,
  'updater.secret' => '',
  'maintenance' => false,
  'theme' => '',
  'loglevel' => 2,
);

I’ve removed the passwords and other login info.

The output of your Apache/nginx/system log in /var/log/____: Nothing in the error.log