If you're using custom email templates instead of using our out of the box templates, then in some cases where the User time zone and the customer time zone are different, the messages sent outside our regular templates were showing the time zone in the User's zone rather than the customer's.
There is a new field on the Appointment Details object named: DateTime in locationTimeZone with API Name: Appointed__DateTime_in_locationTimeZone__c
If you are using our templates that are found hat is found in the Configure>Email tab- you can still swap in the field just to be sure it's consistent. Here's how:
Select the email template you want to edit in the dropdown and then replace this field
Also double-check that the time zone for the location is set correctly in the Configure>Locaiton settings.