If your customers are showing up for appointments you see as canceled, and if there are instances where appointments are automatically canceled a few minutes after they're booked, please note that it's not caused by any errors or bugs in Amelia. 

Amelia can't cancel any appointments on its own. If the appointments were not canceled manually by the client, yourself, another admin, the employee, or any Amelia Managers you may have on your site, the only other option that's left is a link checker.

If you include the %appointment_cancel_url% placeholder in the email, there's a possibility that the link that's sent to your customers is automatically activated by the link checker, and the appointment gets canceled like this.

What link checkers do is they validate each URL that's in the email, and in order to do that they have to visit the URL. Those can be built into the end user's mailing platform, or they could be add-ons for the browser or the email provider (Gmail, Yahoo, Outlook, etc). When they visit the cancelation URL (to check for potential viruses), they cancel the appointment. Unfortunately, there's nothing we can do in this case. The only workaround would be to create a Front-end Customer Panel and explain the procedure in the email, like:

"To cancel your appointment, please log in to your Customer panel, and click on the pencil symbol. There you'll see the "Cancel" option."