How to reproduce:
1. Open the attached project "case_1186887-SpriteAtlasPerforceIssue.zip"
2. Text edit the file 'Atlas.spriteatlas', check the "storedHash/Hash" value
3. Initial hash for iOS is '1781eda60fd1db9c9c8c02ca50aaa6a7'
4. Switch to another build target (Android for instance) and build the project
5. Check 'Atlas.spriteatlas' file again

Expected results: Hash should remain the same.
Actual result: Hash changes between build targets (for example Android, the hash should be: 843ea83e5aa204fe25e7fdf7349968c8)

Reproduced on: 2018.4.15f1, 2019.2.17f1, 2019.3.0f4
Not reproducible: 2020.1.0a18

Edit:
1. Sprite packer mode must be in "Always Enabled" which is the option by default
2. This bug is caused by this fix in Case 1186887