Steps to reproduce the issue

Cronjob triggers Smart Search plugin to index the content:
/usr/local/bin/php /home/[USER]/domains/[DOMAIN]/public_html/cli/finder_indexer.php --purge

Expected result

All batches processed without any errors

Actual result

We see these warnings (in the cron e-mail we receive):

Warning: Use of undefined constant JPATH_COMPONENT - assumed 'JPATH_COMPONENT' (this will throw an Error in a future version of PHP) in /home/[USER]/domains/[DOMAIN]/public_html/administrator/components/com_fields/models/group.php on line 74

System information (as much as possible)

Joomla! 3.9.5
MariaDB 5.5.63
PHP 7.2.16
Apache/2