Pipes are not being numbered

Pipes are not being numbered

I used 'Show Disconnects Options' to see that my pipes, fitting and sprinklers are connected. I've followed the 'List Pipe' and 'Pipe Number' process as per your video. Majority of the time the Pipe Numbers populates all the pipes. Other times it doesn't work. Please can you suggest ways to get the pipe numbered or a way to see why it's not giving numbers to pipe