@Kevin_Z Yes, something like that, but I Checked them through another way (wifi-properties), and double-checked them with command prompt>netsh wlan show interface, the problem has been resolved after...

@Kevin_Z thanks

What about the LAN ports, do they still work for wired connections?

@Philbert I've got Archer T4U AC1300, but instead of solving the problem my big disappointment continues and multiplies... while WN821N shows receive/transmit 300/270Mbps on ISP router and 300/144 on...

BTW, what is the normal and acceptable link speed when I use 5GHz AC1300 adapter (Archer T4U)?

Ok, I do plan to get 5GHz adapter, thanks a lot