FPS cuts in half when in MP

[Groshyr]

So as title says, however details are the following:

-- I use d3d8to9 as my dGPU cannot lock on the game without it, before I always had been capped to 144 fps (which is my screen refresh rate as well) but yesterday I discovered that when I join the multiplayer game on Disco my FPS cuts in half to 65. This happens only in fullscreen mode.
-- I tried disabling vsync and changing multiple settings in nvidia control panel - nothing worked.
-- I'd prefer a solution that doesn't require installing 3rd party tools and other bloatware but changing settings of Windows itself.

Anyone had it, anyone fixed it? Or it's a sign from above for me?