I dont think its the cpu. That i3 is way more than enough...i think turning off direct to disk will help..
Another thing to try is set the fps to exactly 6 (or whatever your frame rate is) in
blue iris and see if that resolves anything..also try increasing your frame rate (in the camera) to say 12-15 and see if there is any difference (make sure to adjust the fps in blue iris as well)
It is also my understanding that windows server prioritizes services so you might want to try running BI as a service..
Finally, if none of this works email support and see what Ken says.. Even if not using direct to disc resolves the issue, i think you figure it out because you save considerable cpu using d2d...