If you recently joined fibre it may pay to do a hard reset on the Apple TV or wipe the network settings and set up fresh.
I recently changed my modem/router (ADSL) and found that the speed on the computer was fine BUT the apple devices (iPad and iPhone) dropped to well under half of what the computer was doing.
In the settings of the router there is an option for what Mode its operating on.
It uses 802.11 and has either a/b/g/n etc after it.
My router was on 802.11 b/g/n BUT after I changed it to 802.11b/g everything came right. In fact everything is running fast again.
You could look at this setting but you may need to consult the manual.
You connect to the router by putting the routers address (something like 192.168.1.1) in the address field of your browser. It’ll ask for a username/password (most normally default to admin/admin – manual will say) and the setting will be there somewhere. Mine was under the Wi-Fi settings.
Put it this way if it helps great….if not you can change it back to what it was.