If you do sudo apt-get upgrade on a Ubuntu box (e.g. a local VVV development environment) and suddenly find your WordPress Dashboard and admin screens are blank (entirely empty grey background except for the admin bar and left hand navigation – because nothing is being printed below the header), you might well need to do:
sudo apt-get install php7.0-xml
This can be triggered by certain plugins, such as JetPack, needing the xml_parser_create() function, which doesn’t exist without that package.
But the error:
PHP Fatal error: Uncaught Error: Call to undefined function xml_parser_create() in /srv/www/example-project/htdocs/wp-includes/class-IXR.php:264
…won’t be visible, and you might start removing plugins unnecessarily (because wiping the plugins will seem to cure the problem…) So I hope that helps.
P.S. when you have something like this, running wp plugin status at the command line (install WP-CLI) is a good idea, as you’ll see all the errors.