It's not area specific, in the way that it only happens at for example: NWAF. I've had it happen West of Krasnostav, in the middle of nowhere etc.. But it does seems to be area specific in the way that when it happens it's like a "bubble" around you that you have to get out of in order to regain FPS. When you've gotten out of the "bubble", it usually works fine running through the same area again, with no loss in frame-rate.