I've not heard of specific issues, but it could be a number of things, one quick way to rule out some of the factors is to whitelist the device and see if there's any immediate improvement.  On the FireStick's client page, take a look at its capabilities and match your radio settings, such as 40MHz channels for example.  And in the "Policy" section of the FireStick's client page you'll see any firewall or traffic shaping rules it may be subject to before whitelisting.  Look at your traffic shaping settings and adjust accordingly on the firewall and traffic shaping page.  Also check minimum bit rates and frequency band, go to your "access control" page and slide the slider up to 12Mbps minimum bit rate for starters and consider making it a 5GHz band only SSID to rule out any issues with the (typically much noisier) 2.4GHz band.  Also depending on which firmware you might try switching between the latest stable and latest beta to see if there's differences with things like 802.11r enabled or not. ... View more