Symptoms
Some TTS-related placeholders (e.g. Ticket_Level_Description, Ticket_Level_ID, Ticket_Message_MessageID, Ticket_Priority_Description, Ticket_Status_Description, etc) appear to be empty in the notifications sent.
Cause
The root cause of the issue is a bug with id #PBA-31672 ("TTS Notification Placeholders").
The list of not working placeholders: Ticket_Level_Description, Ticket_Level_ID, Ticket_Message_MessageID, Ticket_Priority_Description, Ticket_Queue_Description, Ticket_ShortDescription, Ticket_Status_Description, Ticket_Support, Ticket_Support_User_Address1, Ticket_Support_User_Address2, Ticket_Support_User_City, Ticket_Support_User_Country, Ticket_Support_User_Email, Ticket_Support_User_FaxAreaCode, Ticket_Support_User_FaxCountryCode, Ticket_Support_User_FaxExtention, Ticket_Support_User_FaxNumber, Ticket_Support_User_FirstName, Ticket_Support_User_LastName, Ticket_Support_User_PhoneAreaCode, Ticket_Support_User_PhoneCountryCode, Ticket_Support_User_PhoneExtention, Ticket_Support_User_PhoneNumber, Ticket_Support_User_State, Ticket_Support_User_Zip
Some placeholders are filled but not described:, Ticket_Tag, Ticket_Description, Ticket_Subscription, Ticket_Queue_Name, Ticket_Status_Name, Ticket_Priority_Name, Ticket_Category_ID, Ticket_Category_Name, Ticket_Attachment_Link, Ticket_Attachment_Name, Ticket_Description_Status_Changed, Ticket_Email_From
Ticket_FinishDate actually works, but this date is empty in most cases, it is only set if the ticket has been in waiting for customer status for a period more than specified in the setting "Period to autoclose tickets (hours)".
Account_Code is not used at all in the system, so the placeholderTicket_ReportedBy_Account_Code does not work.
Note that TTS module is not going to developed further, it is recommended to review integration with Kayako (refer to kb #126338).