Jittery animation when entering Play mode

Unity: Mecanim Animation

2023.3.X

2023.2.X

2023.1.X

2022.3.X

2022.2.X

2021.3.X

2020.3.X

Reproduction steps:

1. Open user attached project "2d-rpg-demo.zip"
2. Open Assets > Scenes > Gameplay > “Scene_Battle_Dragon” scene
3. Enter Play mode

Expected result: Dragon's sleep animation is smooth
Actual result: Dragon's sleep animation is jittering

Reproduced with: 2020.3.46f1, 2021.3.21f1, 2022.2.11f1, 2023.1.0b8, 2023.2.0a6

Reproducible on: macOS 13.2.1 (Intel), Windows 11 (by user)

Note: Issue reproduces in Editor and Player