Reproduction steps:
1. Open the attached project "ReproProj"
2. Open the “/Assets/Scenes/SampleScene.unity” Scene
3. Select the “Tester” GameObject on the Hierarchy
4. Look at the Inspector to perform the next steps
5. Click the Button with the text “Initialize” to prepare the test
6. Click the Button with the text “Insert Node At Last And Make Connections” to add the 1st node
7. Expand every foldout element in the Inspector
8. See that “Node Id 1” has 1 connection
9. Click the Button with the text “Insert Node At Last And Make Connections” to add the 2nd node

Expected result: Both nodes should have only 1 connection each
Actual result: “Node Id 1” and “Node Id 2” both have 2 connections

Reproducible with: 6000.0.58f1, 6000.2.6f1, 6000.3.0b4, 6000.4.0a1

Testing environment: Windows 10 Enterprise 21H2
Not reproducible on: No other environment tested