Perch Forms not sending notification emails

My site will currently not send any emails when a form is submitted. The form saves fine but the email addresses in the email address field do not get a notification.

The test email is working fine, its just the notifications that do not work.

We have another site on the same server with the same email config (SMTP) which is running fine. Looking at the diagnostics the site where the forms work correctly uses perch_forms v1.8.3 while the site where the email notifications do not work uses the latest perch_forms v1.9.

Is it possible to downgrade from v1.9 to v1.8.3 to see if this fixes the problem.

Thanks