Question Websites, softwares not loading

[Irooo]

Some websites are just not loading on neither of my laptops. And only on one of my home modems.

View: https://youtu.be/wjjgQGxz0Wc?si=WVDQMDAU63SLsVH3

I have done what’s in this video but it didn’t help.
Also on the other network, everything is fine.
I got an Asus rog strix G513
I have recently added a network extender to this modem’s wifi for my 3d printer so I can access it through wifi but I did that a couple of days ago and the problem only appeared today.
Error message: “ERR_ADDRESS_UNREACHABLE”

 

[helpstar]

check if dns is correctly set, scan for malware
restart the extender
restart the modem
update all devices firmware
google for security issues of your modem and your extender
is the modem getting the outer line stable?
anything blinking on extender or modem?

 

[Irooo]

Changed the extender's connection to the less powerful wifi in my house and since that moment, everything on the laptops work. I have no idea how did this work or why. I would still appreciate it if someone could explain this.

 

[helpstar]

maybe the extender is wrongly connected to the modem´s wifi