Reproduction steps:
1. Open the attached project “IKEditorRepro”
2. Open the “Assets/SampleScene” scene
3. Open Window → Analysis → Profiler window
4. Change Profiler mode to “Edit Mode”
5. Enter Play mode
6. Press the “Space” button multiple times
7. Stop recording in the Profiler window
8. In the Profiler search type “IK”
9. Look for “UnityEditor.U2D.IK.IKEditorManager.Initialize” call

Expected result: “UnityEditor.U2D.IK.IKEditorManager.Initialize” is only called once
Actual result: “UnityEditor.U2D.IK.IKEditorManager.Initialize” is called every time the “Space” button is pressed

Reproducible with: 7.0.9 (2021.3.16f1), 8.0.5 (2022.1.24f1), 9.0.1 (2022.2.3f1), 10.0.0-pre.2 (2023.1.0a26)
Not reproducible with: 5.2.6 (2020.3.44f1)

Reproducible on: macOS 13.1 (Intel)