I recently switched to PHP 7 on my development server, which has worked just fine - until now.
Since I updated to PHP 7.0.3-10+deb.sury.org~trusty+1 (ea
PHP 7.0.3-10+deb.sury.org~trusty+1
In Ubuntu 16.04 LTS, with php 5.6, try:
sudo apt-get install php5.6-xml sudo service apache2 restart