PHP fatal errors at device discovery and alert rebuild

Rebuilding alerts from Web UI fail with errors (see attached screenshot)

When running "{{discovery.php -h <hostname>" }}the discovery runs but exits with:

PHP Fatal error: Uncaught Error: Call to undefined function r() in /opt/observium/includes/alerts.inc.php:428
Stack trace:
#0 /opt/observium/includes/alerts.inc.php(409): update_alert_table()
#1 /opt/observium/discovery.php(221): update_alert_tables()
#2 {main}
{{ thrown in /opt/observium/includes/alerts.inc.php on line 428}}