KDL giving two different poses for same configuration

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I'm testing the KDL solver for my URDF file:

• Generating random Joint States1
• Running FK on it and getting Pose1
• Running IK to get the Joint States2

Note 1: Joint states1 and Joint States2 are not getting same and It's normal as one pose can be achieve with multiple configuration.

• I'm running FK again on Joint States2 to get Pose2

Note 2: Pose1 and Pose2 should be same as I'm going in the sequence of FK-IK but I'm getting a constant difference in pose, for example pose_difference.x = 0.02, pose_difference.y = 0.3, pose_difference.z = 0.04

What can be the issue? Please, feel free to write whatever you think can be a problem.