I've just found a fix for my game. I had high cpu priority set on bf5, after switching it back to normal there is no more mouse lag but unfortunately I have bigger fps drops now.
Today i set my cpu priority do normal and disabled razer Cortex, played a round of operations without stuttering
Bumping this up. Can't play anymore due to the mouse lag that doesn't manifest as much as stuttering as just weird sensitivity variations.
If I set my CPU priority to high the sounds starts to cut off, so it's not a solution.
Switching to DX11 drops performance from 90 - 105 FPS to 45 - 60 so not a solution as well.