Same issue here

It seems like I've found a solution for this, if not, let me know!

On your TL-WR941HP router:

1 - Go to your router login page (Usually: 192.168.0.1);

2 - On top menu, click "Advanced";

3 - On left menu, click "Guests Network";

4 - Check "Allow guests to see each other";

5 - Check "Allow guests to access my local network";

6 - Check "Enable Guest Network" and, if you want to, give it a name and configure a WPA/WPA2 password (Very recommended);

7 - Save;

8 - On top menu, click "Advanced" one more time;

9 - On left menu, click "Network" and than "- IPTV";

10 - Let "IGMP Proxy" and "IGMP Snooping" disabled

(Probably, IGMP Snooping will be already disabled. In this case, just disable IGMP Proxy);

11 - Save everything and restart your router.

12 - When configuring your Chromecast, connect it with the Guest Network you just created.

After all, you can connect your device in both wi-fi SSID with no problems. You'll just need, necessarily, the guest network on your Chromecast.

I´m Having the same issue, the only way to keep it working properly is connecting the chromecast to the electric current and then it never will enter on standby mode.

I assume TP link must do a firmware update since the last one is from 2018

Hi! im from Argentina and i just bought a week ago my new router TL-WR941HP an same problem for me, my two Chromecast stop working at all, so i send a email to Argentine Suppport of tp-link and they send me an upgrade Firmware (Beta) and it works!!!

They told me that will send me the final Firmware when its ready.

If someone needs this Firmware, please send me an email: ludime@gmail.com

I will attach a screen shot of my router with the Firmware Beta. 

Same Problem, is a Firmware already?