It seems to me it is something to do with the photogrammetry / Bing maps data and North America / US.
Whatever it is it’s an online aspect of the game. I don’t get any problems unless I do a flight in North America and when I do, after a while I get constantly repeating messages that I’m offline, then reconnected. Eventually the sim gives up and goes offline, the ground looks terrible but the stuttering reduces. If you turn the photogrammetry / Bing maps data back on again then it turns into a slideshow.