Learn More: You may be experiencing networking issues.
Casting a tab requires a good Wi-Fi connection. You may get a better connection by moving your router closer to your TV, or using the HDMI extender included with Chromecast to adjust the position of your Chromecast device.If you wish to connect your Chromecast without using Wi-Fi and have an available Ethernet connection nearby, you might benefit from using the Ethernet adapter.
If you have the option of using a wired connection, or if you have a dual-band Wi-Fi router and can use 5GHz on your computer, this may yield better performance. Please note that your Chromecast must be already set up and connected to your Wi-Fi network and AP Isolation/Client Isolation mode must be turned disabled on your router.
Other applications (e.g. BitTorrent) or devices on your network may reduce available bandwidth; minimizing these may help.