The monologo.svg of the mod_questionnaire plugin is 323x386.
Moodle docs say it should be a Format of 24x24 (https://docs.moodle.org/dev/Moodle_icons)
This leads to a very unpleasant display of the image where it reaches far into the content of Notifications.

Steps

1. Create a questionnaire-activity and activate: "Send submission notifications" -> "Notification only"
2. Create a question
3. Make a submission with a different account
4. The account which created the activity (must be trainer in the course) gets a notification
5. Clickon the Notification bell and chose "See all"
6. you will be forwardet to the Notification page: "<ROOT>/message/output/popup/notifications.php"
7. click on the questionnaire notification
8. the monologo image is displayed far to big

Either the svg is to big and should be corrected or moodle has to make sure at this point that an image is brought and displayed to the right size