@Tony thanks for your response. I did follow your suggestions except could not figure out how to set the QoS speed manually to 1000 Mbps. But no change. Not that it will help but Attaching screenshot...

Had this Archer AX11000 for over 6 months working great. I pay for 1GB connection over fiber and constantly got above 700-800Mbps for both download and upload as measured by the Tether app itself....