Consider the following integral
z = 3*Exp[I*\[Theta]];
n = 20;
k = 1.25 \[Pi];
p = 1.5;
Integrate[BesselJ[(2 n + 1)*p, k*Abs[z]], {\[Theta], -\[Pi]/2, \[Pi]/2}]
However, when I replace Abs[z] with 3, it gives the correct answer:
Integrate[BesselJ[(2 n + 1)*p, k*3], {\[Theta], -\[Pi]/2, \[Pi]/2}]