Strange single client bring down whole network with time scheduling (Parent control)

[webdriver]

Today my home network suffered a strange problem. It causes by enable/disable a single device (a motorola cell phone) from accessing internet at the point - all of sudden the whole internet was down. No matter wired or wireless.
To resolve the issue, I reboot the router, no effect. Factory reset does return the internet but once I restore the settings, the internet down again.
However further investigation found out if disable the parent control/time scheduling the internet is back. Enable on the spot, immediately shutdown internet.
When I scratch head for why parent control kill the internet, and by removing the cellphone from the control list (when other devices still in blocking/time limit list) and internet does recovered!

Not sure what happens but IT'S REALLY strange.

Anyone can give some analysis what could be the problem?

Router is ASUS AC86U running official 386. latest fw.

 

[L&LD]

When 'extremely weird' things like this land, there is no analysis needed. Time to do a full reset without restoring saved backup config files.

Best Practice Update/Setup Router/AiMesh Node(s) 2021

 

[dev_null]

It's been reported that some blocked Android devices flood the network with connection attempts when they are blocked (probably depends on the firmware and apps loaded). I have witnessed this myself with certain devices on AOS 7 and earlier (not so much in the later versions) when ad-blocking is in place (both Merlin and FreshTomato). My approach was to put them onto the guest network with AP isolation, which helped to a degree. I also found that reducing the TCP Timeout: Established and TCP Timeout: time_wait (both by 50%) helped.

Try removing this device and see if that restores stability.