I just installed a Archer A9 to replace a 10 + y.o. Netgear WiFi router. It really helped with my LAN connected laptop. But I am trying to figure out why out of 3 android devices, all less than a year old, all running on Android 9. Only one can see the 5Ghz WiFi connection. The two that are blind are a Samsung J series Phone and an Chinese Off brand tablet from Amazon. The sighted device is a Kindle Fire 8. 

I've run through all the settings in the Android devices and the setup of the router. Done the deleting and rebooting, cache cleaning. gave individual SSID names to the 2.4 and 5 on the host and guest. After posting this, 3 hours doing internet search, it's the chair, beer and  YouTube research. Which turns into watching squirrel videos.

I live in a foreign country, Southeast Alaska. Any ideas, even the ones I have already tried will be greatly appreciated. I hate getting beat by a problem that should have a solution. It took me two days, but my new Kindle Fire 8 HD 2020 is now working with Google. The Play Store and Chrome browser are playing well with Amazon Appstore and Silk Browser.