This is a bit of a weird one, since it's an interesting variation of a much more common issue with other games, that stems from Windows. The Desktop Window Manager in Windows 10 is very bad at handling differing refresh rates so if you put any video material up on a slower secondary monitor (stream, video, OBS, another game, stream alert box, etc), most windowed games on the primary monitor begin to stutter periodically, in the form of dropped display frames. Even games on an entirely fixed timebase (e.g. Touhou games) only drop displayed frames and continue to run at the same speed. The FP2 Sample Version does not exhibit this behaviour, and instead slows down periodically. While my knowledge on the subject is somewhat limited, I would guess that this behaviour has something to do with the game's specific deltatime implementation and how it deals with this specific kind of stutter.
This is a bit of a weird one, since it's an interesting variation of a much more common issue with other games, that stems from Windows. The Desktop Window Manager in Windows 10 is very bad at handling differing refresh rates so if you put any video material up on a slower secondary monitor (stream, video, OBS, another game, stream alert box, etc), most windowed games on the primary monitor begin to stutter periodically, in the form of dropped display frames. Even games on an entirely fixed timebase (e.g. Touhou games) only drop displayed frames and continue to run at the same speed. The FP2 Sample Version does not exhibit this behaviour, and instead slows down periodically. While my knowledge on the subject is somewhat limited, I would guess that this behaviour has something to do with the game's specific deltatime implementation and how it deals with this specific kind of stutter.
https://www.youtube.com/watch?v=6nFERihRi6M
I'm aware that this is a bit of a strange and specific scenario, but it at least warrants a small look.
Some system information since it's pretty relevant here:
i5-3570k 4.2ghz AMD Radeon R9 290 8GB DDR3-1600 BenQ XL2411Z at 120hz (primary monitor) Philips 15" 4:3 somethingsomething (I'm sorry it's very old) at 60hz (secondary monitor) Windows 10 Professional