Archer A6 - blacklist simply doesnt work

When I blacklist devices, they still find their way to the internet. Any ideas why that is?

My setup:

Modem from provider uses thernet into my archer A6. My archer A6 then uses ethernet into a large wired switch.

My archer A6 is in router mode. I dont use the wifi on my archerA6 because I have a deco mesh system (plugged into the switch )