Change 5G channel on your router. Usually there are certain channels that the router can work with. Channels in band 1 or band 4 recommended

Dude, what's the model number? That message is not from TP-Link it seems. What device do you use? Why it need packet fragmentation?

If you configure it as wireless router, you can still connect to the wireless network and login web interface to check settings. Usually we need to check WAN status if internet looses. And also check...

Do you notice the light turn red? If so the slave deco lose connection from the main deco or internet. Maybe it's the distance or interference. Are all your decos working as router or access point?...

There is no Kensington lock slot or something like that on M5. So, to physically lock it, you can put it in a box and lock it, which may however dampen the signal...

Change inside the printer panel. There are access control and parental controls. You can use either one to block device from internet. Whether it will block from LAN access, I don't think so but I...