David Anderson on "[Plugin: UpdraftPlus Backup and Restoration for WordPress] "proc_open() has been disabled for security reasons""

Sounds like proc_open() isn't just disabled on your web server, but causes PHP to crash if tried. Try adding this to your wp-config.php:

define('UPDRAFTPLUS_MYSQLDUMP_EXECUTABLE', '');
define('UPDRAFTPLUS_NO_BINZIP', true);

Best wishes,
David