Well personally, I’ve been having the default SC2 generic one for years, and as I notice Poutree had a custom one while he had only one game played on US/NA I figured playing one NA ranked game would solve the issue. And it did for me :
https://static.starcraft2.com/starport/d0e7c831-18ab-4cd6-adc7-9d4a28f49ec7/portraits/14-14.jpg
Now if you have recently played NA ranked games, it might indeed not be the issue at hand in your case. Maybe it’s related to you being an MVP on current forums version ? I’ve not seen others MVPs in SC2’s forums, so we lack of comparison points.
Does your alt account also has the MVP status ?
EDIT : reported the issue in the bugs section. 