AC-86U can't block internet access for one device

Hi,

I would like to block one device's internet access but every time I blocked one device's internet access, all devices lost internet access at the same time.

what I did:
Selected that particular device from "client list" and then switched on "Block internet Access" and applied changes.

It seems to me block one device will also block all devices connected to the router. Did I miss something?

I am using AC 86U with firmware version:3.0.0.4.384_81352-g9910ab0.

thanks.