When I round A-mark (windward), and release my main and jib, the jib boom does not go out easily, I feel like I have to push it out with a paddle! Even in medium wind strengths.
The line type you may be using for the jib might be too thick, and/or the wrong line type. The line may also be strung incorrectly through the cheek blocks and blocks. Check the line, trace the line.
Now I saw a weird one recently where the jib boom swivel was mounted upside down on the deck. Putting it right side up made a huge difference!