I am having this problem as well, also with the AT2020 under Windows 8.1! The troubleshooter did nothing and Audio-Technica hasn't gotten back to me (although even if they did I don't know what they could do since these microphones are practically plug 'n' play.)
Please, if you can, work on a fix for this! I am a YouTuber and voice actor and desperately need my microphone to be working optimally, and I unfortunately have no means by which to roll back to Windows 7! I can make it work for now but as far as I can tell my mic will not be performing optimally until a fix is produced!