How to reproduce:
1. Open the attached "1297288 repro" project
2. Open the "Test" Prefab from Assets > Scenes folder
3. Select the "New Sprite" GameObject from the Hierarchy window
4. Increase the Order in Layer value of the Sprite Renderer Component to 10 in the Inspector window

Expected results: the Sprite is rendered above the white Image because the Order in Layer is higher
Actual results; the Sprite is rendered below the white Image

Reproducible with: 2020.1.0a5, 2020.2.1f1
Not reproducible with: 2018.4.30f1, 2019.4.16f1, 2020.1.0a4, 2021.1.0a1, 2021.1.0a10, 2021.2.0a1

Notes:
-2 Sprites in the same Prefab interact correctly and respect each other's Order in Layer.
-2 Canvases in the same Prefab interact correctly and respect each other's Order in Layer.
-Sprites are always hidden under the Canvas in the Prefab Mode no matter what the Order in Layer is