How to reproduce:
1. Open the attached “SplinesBug.zip” project
2. Enter “repro” Scene (Assets > Scenes)
3. Enter Play Mode
4. Open the Scene window
5. In the Hierarchy window, select “Spline” GameObject
6. Select Spline in the tools menu
7. In the Scene, select two Spline knots
8. Press the “Link” button in the Elements Inspector window
9. Observe the Console window

Expected result: “Spline Changed” is logged
Actual result: No logs

Reproducible with: 2.1.0 (2021.3.29f1), 2.3.0 (2021.3.29f1. 2022.3.6f1, 2023.1.6f1, 2023.2.0b2)

Reproduced on: macOS 13.4.1 (Intel)

Notes:
-also reproducible with the “Unlink”
-not reproducible with the “Join” and “Split”