Google Forms have a daily sending limit for email notifications. If you have too many people responding to your Google Form in a 24 hour period, the daily quota may be exceeded and no email may go out to the new form respondents.
If emails were not sent to any of the form respondents, you can manually trigger the email notifications inside the Google Forms add-on. This is available with the premium version.
Before you trigger emails, go to your Gmail sent items and confirm that emails have not been sent to a particular form respondent else you may end up sending a duplicate email to the same person.
Then open the Google Form, go to the addons menu, choose troubleshoot and here you’ll see an option to resend email notifications.
Click the “Resend Notifications” button and you’ll get a list of all form responses received in the reverse chronological order (newest listed at the top).
You can click “View Response” to check the original responses while the “Send Email” button will actually trigger the instant email notification.