Once in a while a run in to an orphaned tty session. Somebody logged on by means of serial cable, and left while forgeeting to log out.

ninja@someswitch> show system users  
fpc0:
--------------------------------------------------------------------------
11:47PM  up 252 days, 14:55, 2 users, load averages: 0.69, 0.58, 0.57
USER     TTY      FROM                              LOGIN@  IDLE WHAT
root     u0       -                                08Aug22 252days cl             
ninja   pts/0     somejump-host   11:47PM     - -cl            

The way to get rid of this is easy. But beware this might take some time. 30 seconds to a minute.

ninja@someswitch> request system logout terminal u0

And check if the phantom user is gone;

ninja@someswitch> show system users  
fpc0:
--------------------------------------------------------------------------
11:49PM  up 252 days, 14:56, 1 users, load averages: 0.53, 0.55, 0.56
USER     TTY      FROM                              LOGIN@  IDLE WHAT
ninja   pts/0     somejump-host    11:47PM     - -cl