It will be necessary to do this any time you try and start up the ATV2 after it has lost power for any reason.
If when you jailbroke the ATV2 using SeaonPass you did not explicitly elect a particular firmware version then it would ahve defaulted to the 5.3 release (which is the latest that SeasonPass can currently jailbreak).
Since you’re running untethered then you don’t have to do that step (this thread was started when 5.3 was still tethered). After the untethered jalbreak, it can sometimes take a few minutes for the ATV to first boot, give it time. If after 10 minutes it doewsn’t boot, unplug it and replug it. If it still doesn’t boot then re-jalbreak it.
Did you ever get a answer for your atv2? If so, could you please share with me. Today my atv2 just rebooted in themiddle of playing a movie. Now it reboots to a black screen after showing the Apple logo. Light blinks stop then blinks again. This sound like what you experienced. Did you resolve your problem? Has anyone else had this problem? Do I have to start over with a new jailbreak? I was 4.4 untethered, 12.2 or 3 frodo.