Hello Raj,
As far as i know, this event is sent from Host terminal. I receive an USB_APP_CDC_DTE_ACTIVATED event every time i open a new terminal when using TeraTerm, but i do not receive more than one event eventhough i received more than 280 bytes.
You should pay attention on your Host terminal rather than USB CDC example.
I hope this can help you.
Best Regards,
Isaac