@diporif Usually the exclamation mark symbol means "Poor network". Can you put the RE450 closer to your router and check if the symbol disappears.

@h-maulwurf That's really odd. Your laptop, mobile or tablet doesn't know that the Archer C6 WAN port is unplugged. So there's no way a laptop to ignore this knowledge but a mobile or tablet to...

@h-maulwurf There's an IP address issue as seen from your last screenshot. Your office subnet is 192.168.1.0/24, but on the last screenshot the router is with IP address 192.168.0.1 (different...

@Hamza-Haidar What about LAN IP address of the AX55 - is it set to Dynamic IP or a Static IP ? If it's set to Dynamic IP then set it to a Static IP (192.168.99.254) and test again for these DHCP...

@Hamza-Haidar This has been seen before on a different models in AP mode. What is your DHCP setting ? If it's on 'Auto' then set it to 'OFF' and test again. Check this story - there's no need to...

@xiaohan On of those two probably have fixed the issue - upgrading to firmware Archer C7(US)_V2_180114 or rebooting the router.