Stacking Effect, Twin Queen Set vs. Gwanfara's Ghost Quiver

Testing both the set and the quiver at the same time only using hunting arrow (which should provide 1 stack for both of them), at the time I reach 25 stacks for the set, I only get like 10 or 11 stacks for the quiver. Why is this happening? Note that I'm using the Fortified String effect of hunting arrow (it penetrates the first target it hits).

PS: if this is not clear, I can show it in a video, just don't feeling doing it now.

EDIT: I have noticed that as long as the counter has just started ( pointing at 1 m "1 minute"), the stacks don't increase even if you hit critical hits with hunting arrow, but once the counter goes to 59 s (59 seconds), you get stacks, so basically we get a 1 second delay everytime we get a stack. Also I'm still waiting for some reply