I understand that your issue is with the automated replies that are supposed to insert the guest name. There should be people here who can help, can you perhaps send a screenshot showing your message where the code is inserted?
I also have this issue whenever I update a Welcome message in the app. Even if a short code is entered and saved, it just deletes the brackets and sends "guest first name" which looks super unprofessional. This has been an ongoing issue for all of my listings, so I decided to take out all personalizations. I've also found that Airbnb "Support" for hosts is remarkably frustrating and not helpful in almost any situation.