My colleagues are getting multiple reminder emails sent to them all at the same time

I checked this form https://www.jotform.ca/form/92807298391267 and found that there were multiple submissions from the same users. Also, the submissions were registered from the same IP address which means that the submissions were initiated from their own network / computer.

If they reload the cache of the thank you page, it triggers the submission again. To prevent this, try implementing unique submissions feature to your form https://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form.

Let us know if you have any questions or if you need further assistance.