To reproduce:
1. Open attached project "New Unity Project.zip" with Unity 2017.4
2. Select "New Sprite Atlas.spriteatlas" sprite atlas
3. Observe in the Inspector that Allow Rotation and Tight Packing are false
4. Close the project and open it with Unity 2018.2 or 2018.3 or 2019.1
5. Select the sprite atlas and observe in the inspector that the values are true
6. Navigate to Project folder and open the sprite atlas with any text editor
7. Observe as these values are set to 0(false):
enableRotation: 0
enableTightPacking: 0

Expected result: when upgrading Unity version, Sprite atlas values are kept
Actual result: the values shown as true, even though in the serialized version of sprite atlas the values are false

Reproduced on:
2017.4.0f1 / 2017.4.13f1 - 2018.2.13f1, 2018.3.0b6, 2019.1.0a5

Notes:
If the project was created on 2018.2 and then upgraded to 2018.3 or 2019.1, the issue doesn't reproduce
If 2018.2 project opened with 2017.4, getting the same behavior, Inspector shows true, serialized asset shows false.