Kevin SG wrote no matter which web browser, the management interface will meet the same issue? Is the time setting correct? If the DHCP server can't assign ip address normally, it may lead issue 1...

Model : Archer C1200 Hardware Version : Not Clear Firmware Version : 1.0.0 Build 20180208 rel.57928 (EU) ISP : Unifi TP-LINK Archer C1200 Device Information Firmware Version: 1.0.0 Build 20180208...

which version for your router TP-LINK Archer C1200? if v1, than u may update the firmware to latest version. my router has updated the firmware, now is supported for TR069 Firmware Version: 1.0.0...

all setting is correct, already try other router, no problem. both ddns also same error

sure, it will suddenly no responding, try many browser, but sill like that, until need to restart the router

Model : Archer C1200 Hardware Version : Firmware Version : 1.0.0 Build 20180208 rel.57928 (EU) ISP : TM Unifi Firmware Version: 1.0.0 Build 20180208 rel.57928 (EU) Hardware Version:Archer C1200 v1.0...