If enemies are too close to you or the projectile cast/attack point, the projectile does not hit them. I'm using stings of krearion and Arctic Spear and if enemies come too close to you or the spear cast point, they do not hit the enemy. (It's same with pistol attack against destructible objects like boxes, barrels etc. I do not use pistol attack against enemies though.)
Also sometimes they do not hit the enemy at all, Even though they pass right through them, no matter the distance. Sucks to die to mob of trash tier enemies that you can't kill even though I should be able to one shot them.