For some reason settings I copied to use as my crosshair not working properly.
For example, I tried to use this one:
https://www.deadlockit.com/crosshair/123-15
Copypasted this in console:
citadel_crosshair_color_r 0;
citadel_crosshair_color_g 255;
citadel_crosshair_color_b 255...
I can confirm it dont give you stacks if any of your teammates get the kill but if you do the kill then you'll get it. Which feels kinda weird because its pretty rare situation when you use bird - not killing your target - then kill it anyway in 3s window.