How to reproduce it:
1. Open the user's attached project 'WebGLAnimation.zip'
2. Load the 'repro' scene
3. Build on WebGL Standalone (File > Build Settings > WebGL > Build and Run)
4. Click and observe the plant on the WebGL player

Expected result: The plant swings, Button's OnClick() triggers Animator.Play()
Actual result: The plant doesn't swing, Button's OnClick() doesn't trigger Animator.Play()

Reproducible with: 2020.2.0b11, 2020.2.3f1, 2021.1.0a1, 2021.1.0b4, 2021.2.0a1
Not reproducible with: 2019.4.19f1, 2020.2.0b10, 2021.2.0a2, 2021.2.0a3
Could not test with: 2018.4.30f1 (2D Sprite is not introduced)

Notes:
- Not reproducible on Win Standalone build