How to reproduce:
1. Open the attached project "SpriteEditorBug.zip"
2. In the Assets folder, locate the Square sprite
3. Select the sprite and click the 'Sprite Editor' button in the Inspector
4. Change the Pivot Unit Mode to Pixels
5. Enter Play Mode
6. Exit Play Mode

Expected result: The Pivot Unit Mode remains set to 'Pixels'
Actual result: The Pivot Unit Mode has changed back to 'Normalized'

Reproducible with: 2019.4.29f1, 2020.3.14f1, 2021.1.14f1, 2021.2.0b3, 2022.1.0a1 (1.0.0)
Could not test with: 2018.4.34f1 (package not supported)

Note:
1. In 2022.1 the Sprite Editor view will split after entering Play Mode