Sounds like your Samsung TV doesn't announce itself with an ALIVE message, or its announcement doesn't make it across your network.
PMS sends an ALIVE message when it starts up, then 10 seconds later again and then 20 seconds later again. After that, PMS only sends an ALIVE message every three minutes.
It appears your TV receives the PMS ALIVE messages and answers them, but PMS does not receive your TV's ALIVE message.
Try waiting for more than three minutes to see if the TV appears in PMS.