For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
See Announcement
Please post subscription issues here
We have resolved the issue with the J! updater and this will be fixed in the next release.
// Require the abstract plugin class
require_once(COM_FABRIK_FRONTEND . '/models/importcsv.php');
// Require the abstract plugin class
require_once(COM_FABRIK_FRONTEND . '/models/plugin-cron.php');
require_once(COM_FABRIK_FRONTEND . '/models/importcsv.php');