when we change the domain through the modify an account menu, we check after the changed domain we see in the zone menu for the FTP record to be deleted, is that right?
Internal case CPANEL-23771 is open to address an issue where modifying the main domain of a cPanel user account via WHM >> Modify an Account removes the "ftp" A record entry from the domain's DNS zone. I'll monitor this case and update this thread with more information as it becomes available. In the meantime, the temporary workaround is to use WHM >> Edit DNS Zone to manually add in the "A" record for "ftp" after modifying the account.