One of the default settings of Starred is sending a friendly reminder to your contacts, 6 days after sending the invitation. Obviously, your contacts only receive this reminder if they didn't submit their feedback in these 6 days. Here, you can read more on how to change these settings.
Accidentally forgot to turn this reminder off? No worries, you can disable the reminder within 4 days after the invitation!
Go to the overview in Forms and click on Invitations in the drop-down menu on the right of the feedback form. Click on the sender of the invitation batch to see the details of this invitation batch. Here, you find a red button saying Disable reminder.
Clicking this button allows you to disable the reminder mail. Remember, you won't be able to turn it back on!