Starting 21.4 Junos OS, the "show pfe statistics traffic" command can no longer be run on SRX4200. As an alternative, customer can run the same command from the shell to obtain the needed information.
To access VTY on SRX4200, you can use any of these options:
1) Enter the shell and then VTY:
> start shell
> vty fpc0
> show pfe statistics traffic
2) Request the vty command to be run from operational mode:
> request pfe execute target fpc0 command "show pfe statistics traffic"