I see this, too. For me, it will happen for the first time a few seconds after loading a flight, at about the same time when I got the AS16 weather update message (until I disabled AS messages, in order to get rid of the popup message window). That's why I assume that, at least for me, the "drop outs" are related to something like AS16 or UT2. I guess I'll try to pay more attention to whether the drop outs happen in a certain interval and whether I can correlate that to the AS16 weather update interval or something like that.
I do have a ridiculous amount of addons, and I'm often flying close to 30fps because eye candy.