Why don't POE cameras sometimes display pictures?

Anyone who does monitoring should know that there are two kinds of cameras, power supply and POE power supply. Generally, the power camera is relatively stable, but it needs to pull the power cord separately or use a comprehensive cable to connect the power supply. POE power supply only needs to pull an eight-core network cable, and the other end can use POE switch or POE video recorder to supply power to the camera.

However, the power supply of POE cameras always takes a while, and some cameras don't display pictures, or they can't be found in video recorders. The easiest way to eliminate this problem is to replace a new camera, plug in the power supply, let the video recorder search normally, and automatically add a new camera.

Old cameras can be used by restoring the factory settings through tools, or they can be added manually, and the camera IP can be entered. However, if the factory settings are not restored, it is generally difficult to be searched by video recorders and images cannot be displayed. What is the reason? That great god can enlighten me.