So my normal sequence of casting rapid was
1. target mob
2. hit auto
3. cast rapid
After that the first hit after rapid was casted did not hit even though the damage numbers popped up. I noticed that in between hitting the auto button and casting rapid, the animation for my character using a auto was about halfway through. So basically casting rapid shot cancels the auto, and the auto that was canceled is fired after rapid shot is finished casting. Its sort of like the glitch where you auto a mob, but move away while the animation is going and you still fire the arrow but it doesn't actually hit.
So after that i changed the sequence of casting to:
1. target mob
2. cast rapid
3. hit auto (while rapid was loading)
This got rid of the first hit not doing any damage but theres a slight delay after casting to where you actually begin to fire arrows. Also it seems that rapid shot works fine in pvp. I tested this multiple times on mobs in the OW and came up with this theory. It would be great if other rangers could test this too.
