GeorgeBitt One of our engineers have tested Chromecast v1 and v2 with WNDR4300v2 in AP mode and didn't get the same result as yours.

Everything is working on our end. There are no special settings set on the router. And again it didn't matter whether IGMP is enabled or disabled, Chromecast is working fine.

You may want to check your settings by using the guidelines below:

Your computer is on the same WiFi network as the Chromecast
Make sure you're suing the power adapter plug that came in the Chromecast box and not USB powered
Use the extension cable included in your Chromecast box
Try the official Chromecast Troubleshooter. See this link.
Install the latest FW version of the router
If you're using a dual band router, ensure you are connecting to the 2.4Ghz network for Chromecast and make separate AP names for each 2.4Ghz and 5Ghz networks
Select the best channel and disregard using the Auto channel selection
If you have MAC filtering enabled on the router, add the MAC address of your Chromecast
Chromecast will not communicate with your router if you have AP/Client isolation enabled
Chromecast will not communicate with your router or computer if any VPN or Proxy servers are turned on both of your router and computer
Enable UPnP for easy network discovery of the Chromecast
On Verizon routers, disable IGMP snooping

Let us know what happens.

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