How to reproduce:
1. Open the "SetAnimEventTest" project
2. Open "TestAnimCtrl" Animator Controller from the Assets folder
3. Select "Test" State of the Animator Controller in the Animator window
4. Press "Test" > "Open Window" in the menu bar
5. Press the "Start" button in the "Animation Clip Event Editor" window

Expected result: Motion of the "Test" State remains "idle" Animation Clip
Actual result: Motion of the "Test" State is lost and resets to None

Reproducible with: 2019.2.1f1, 2019.2.21f1, 2019.3.23f1, 2020.1.0b9, 2020.2.0a12
Not reproducible with: 2018.4.23f1, 2019.2.0f1

Notes:
-This issue occurs only when setting the clipAnimations for the first time after importing the model, on further iterations of the Script, Animation IDs don't change and references are kept.