Nextcloud 14.04 stopped working on me. I was getting a blank page on my nextcloud website. I found the following error message in my nextcloud logfile:
"Error: Call to undefined function OC\\App\\simplexml_load_file() at \/var\/www\/cc.com\/nextcloud\/lib\/private\/App\/InfoParser.php#64".
It appears the problem was when php was updated from 7.2 to 7.3 however the apache2 webserver was trying to use the older php7.2 module and php7.3 module was not enabled. The solution is to disable the php7.2 and enable php7.3 module for apache2. The following commands are entered into the terminal.
Disable the apache2 module php7.2
sudo a2dismod php7.2
Enable the apache2 module php7.3
sudo a2enmod php7.3
Restart the Apache webserver and show it’s running status
sudo systemctl restart apache2 & sudo systemctl status apache2
I found the following site helpful: https://tecadmin.net/switch-between-multiple-php-version-on-debian/
The server was Debian testing/sid. 2019-0110