This issue is normally due to the Registration Page Layout.  If your code is not configured to handle modern/responsive layout it will not produce the ticket description.  You would either need to update the code to handle in the Page Wrapper/stylesheet or set the event to a classic page layout.  To change to the classic layout:
  1. Select edit on the event.
  2. Select Step 3 Configure Additional Information.
  3. Step 8 Registration Page Layout can be changed to "Classic".
Once this is changed the ticket description should populate correctly when selecting the ticket type.