Nmap scan is not showing all devices in my network

I have an Android device that runs Android9 and also another Android device that runs Android6 on it. I shared Android9’s internet to Android6 through a wifi connection. Then I shared the Android6’s internet to my computer (runs linux) through USB Tethering option. Then on my computer, I run the command sudo nmap -sn <my_network_address>

It only showed my Android6’s ip address and my computer’s ip address. It does not show my Android9 on that list.

I want to know why do this happen.

Thanks in advance.