Why the viewport is black with VCam actor enabled

Hi,
I followed the VCam official document (Controlling a Virtual Camera Actor using Live Link in Unreal Engine | Unreal Engine 5.5 Documentation | Epic Developer Community) step by step,but the viewport is black with Vcam actor enable.I switched from 5.3 to 5.4,the problem still exist.

I spend hours searching solution with Unreal Engine Forums、google and youtube, unfortunately I failed.