Google Chromecast will not connect to Chromecast - Non technical user!

[Victoria222]

I have an ORBI RBR50 - it will not connect to my Google Chromecast - If I flip over to my old Sky Router Wifi (which luckily I still have) then Chromecast work fine. 

To be honest I have this issue with a number of wifi devices in my home when I try to use the Orbi RBR50, I am just about fed up with the entire system as susrely these things should be pretty much plug and play now a days. 

I have emailed support at Orbi about some of my previous issues but no response.

I am not technical and to my knowledge should not need to be to set these things up.

The Orbi App says the security is expired but I do not want to spend $70 on this when the router does not work well anyway - if we have to spend this annually to use the ORBI it would have been nice to know before purcase of the router.

I am thinking of dumping the ORBI due to the fact it is so needy and the support so dreadful and buying Google Nest WiFi but I am worried this will not reach our garden studio where I work?

Idea or thoughts appreciated! 

Thanks, Victoria 

[FURRYe38]

What Firmware version is currently loaded?
What is the Manufacturer and model# of the ISP modem the NG router is connected too? If there is a built in router here, 
This would be a double NAT condition which isn't recommended. https://kb.netgear.com/30186/What-is-Double-NAT
https://kb.netgear.com/30187/How-to-fix-issues-with-Double-NAT
Couple of options,
1. Configure the modem for transparent bridge or modem only mode. Then use the Orbi router in router mode. You'll need to contact the ISP for help and information in regards to the modem being bridged correctly.
2. If you can't bridge the modem, disable ALL wifi radios on the modem, configure the modems DMZ/ExposedHost or IP Pass-Through for the IP address the Orbi router gets from the modem. Then you can use the Orbi router in Router mode.
3. Or disable all wifi radios on the modem and connect the Orbi router to the modem, configure AP mode on the Orbi router. https://kb.netgear.com/31218/How-do-I-configure-my-Orbi-router-to-act-as-an-access-point and https://www.youtube.com/watch?v=H7LOcJ8GdDo&app=desktop

Is the Orbi wifi using the same SSID name and PW as on the prior router? You can use this same configuration.

What is the size of your home? Sq Ft?
What is the distance between the router and satellite(s)? 30 feet is recommended in between RBR and RBS to begin with depending upon building materials when wirelessly connected. https://kb.netgear.com/000036466/How-far-should-I-place-my-Orbi-satellite-from-my-Orbi-router

What channels are you using? Auto? Try setting manual channel 1, 6 or 11 on 2.4Ghz and any unused channel on 5Ghz.
Any Wifi Neighbors near by? If so, how many?

Try enabling Beamforming and MIMO(MIMO may or maynot be needed) and WMM. Under Advanced Tab/Advanced Settings/Wireless Settings

Try disabling the following and see:
Armor, Circle, Daisy Chain, Fast Roaming, IPv6 and Set 20/40Mhz Coexistence to 40Mhz only. Set Short preamble instead of Long preamble modes. Save settings and reboot the router and satellite(s).