website seems to be cancelling appointment

This was the email from Tanya

From: Tanya <tanyaclayton@aol.com>
Date: Mon, Jul 4, 2016 at 1:23 PM
Subject: Another false removal
To: Kim Adamof <kadamof@gmail.com>

Hi this was sent to Liz
She didn't cancel
Rrr I have know idea what else to do
If u have ideas that would be great

Sent from my iPhone Tanya

Begin forwarded message:

> From: Muse <webmaster@musehairdesign.com>
> Date: July 4, 2016 at 11:32:59 AM EDT
> To: webmaster@musehairdesign.com
> Subject: Removal notification
>
> An appointment removal notification for ID 1249 has been sent to your client:
>
>
> Dear Liz truitt,
>
> We would like to inform you that your appointment with Muse on July 5, 2016 5:30 pm has been removed.
>
> Here are your appointment details:
> Requested service: Full head of foils
> Date and time: July 5, 2016 5:30 pm
>
> Kind regards,
> Muse

These are the active plugins:
Akismet (now deactivated)
Alpine PhotoTile for Instagram
Appts+
Backupbuddy
Genesis simple edits
google analytics
Gravity Forms
Wordfence Security
WPMU Dashboard

I have attached a screenshot of the log showing that as soon as the email reminder is sent, there is a cancellation.

In the past, we've been having this issue on and off. It's random. Always happens after someone gets their email reminder. At first I thought people were clicking the cancel button in the email thinking they are confirming, however, I have changed the email notification to highlight the fact they are cancelling, not confirming; plus we are sending the cancellation email so they know their appt was cancelled.

All plugins are up to date.

Do you know of any plugin conflicts? I can't recreate the problem since it's random to figure out which plugin might be the culprit.