D9131A will only print the header over and over for every alarm while in fire walk test.
The header is printed when the power for the D9131A is cycled. Make sure that the power for the D9131A is not connected to Relay C or switched aux. Connect power to SDI power, terminal 32. Connecting power to switched aux or Relay C will cause power for the D9131A to cycle following every alarm as the panel attempts to drop power to smoke detectors in order to reset them.