No squawk alert

[yang]

My ANRB received one aircraft which mode-s code is 19999B and squawk is 7700. I have received the mode-s alert but not received the squawk alert. I am sure that the mode-s code 19999B and squawk code 7700 both are in my alert list. Why no 7700 alert? Does anyone know what's the problem?

Thank you.

Yang