I get this on the setting page, both as admin and as my user (also an admin). I can find nothing via search or the magic google. Complete text of message:
“WARNING: /var/www/html/plugins/API/API.php(401): Notice - compact(): Undefined variable: idGoal - Matomo 3.5.1 - Please report this message in the Matomo forums: https://forum.matomo.org (please do a search first as it might have been reported already)”
Fresh install; Matomo version: 3.5.1, MySQL version: 5.5.56-MariaDB, PHP version: 7.3.0beta2.