Q: I get this error when trying to mirror Macbook Pro to the newest Apple TV

If AirPlay disconnects by itself, your wireless network might be too busy or have too much wireless interference to maintain the AirPlay connection. Learn how to troubleshoot Wi-Fi connectivity issues. The manual of your network router might have additional suggestions for maintaining a strong and fast connection with your devices.

From this support article

Use AirPlay to display video from your Mac on an HDTV