The wifi on the ATV is a bit annoying.
In a wifi network where the 2.4GHz and 5GHz are named the same, your typical "mesh" setup, the ATV has a tendency to hang on 2.4GHz. In particular after a power outage, or when you reboot the wifi after the ATV is on. The 5GHz takes a bit longer to come online after reboot due to interference checking. Meaning that for a period of time the network will only broadcast on 2.4GHz. The ATV connects to 2.4. And stays there. It does not send a single probe request on 5GHz (unlike iphones, ipads, macs which are very well behaved in that regard). Meaning the ATV does not self select into 5GHz when its available. And the wifi system does not get any hint (lack of probe request) that the device can indeed support 5GHz and therefore most of the system's wont force steer the ATV to 5GHz. Going to sleep and wake up does not toggle a new wifi scan from the ATV. Power off/on will.
Not really a answer to your problem - just another problem.
-Erik