When I move the pop-out Objective window to a 2nd monitor, I start getting a bad stutter. It stops if I move the pop-out back to the same monitor as the sim. This began with the Beta for Update 8 and is still persisting after the official release of Update 8.
Click with mouse back in the first monitor at least once after having moved the pop-out window to the second monitor. Even any other application external to MSFS will produce this effect. You can also lose 10fps in game just by having mouse focused out of main monitor (e.g: if you are running a moving map application or checking your flight charts in the second monitor). This is a really old issue persisting since the early releases of game indeed.
Sadly, that’s not the issue. I tried your suggestion but the stutter persists no matter what I do until I move the window back to the main screen. And this specifically started with Update 8.