@David-TP I tried to downgrade back to 1.6.1 but the problem still exist. I changed the router for testing and it can connect to baidu com. Quite sure that is the Deco M5 problem. I recalled that at...

@David-TP Yes I had tried changed to Google DNS and 1.1.1.1, updated the domain pan.baidu to whitelist but still not success. Any chances to rollback the firmware for me to testing?

After upgrading to 1.6.x I found out that there are some domain I cannot get in, e.g. pan.baidu. I checked the Deco app, and ensure that firewall didn't blocked and no parental control had setup.