To reproduce:

1. Download and open attached "SpriteAtlas ETC Variant Size Issue.zip".
2. Make sure Build Settings are switched to Android platform.
3. Ensure "Test 66" is only Atlas version checked for "Include in Build" option.
4. Enter Play mode.
5. Notice the corrupted sprites in the Play mode and in the preview.

Expected result: Sprites Atlas is scaled and sprites are displayed correctly, maintaining correct aspect ratio.
Actual result: Sprite Atlas gets corrupted, it's aspect ratio is not maintained. Assertion failed error comes up in the console.

Reproduced with: 2017.3.0b3, 2017.2.0f3, 2017.1.1p4, 2017.1.0a5.

Notes: Sprite atlas was introduced in 2017.1.0a5. Error is thrown when Variant atlas Scale is changed to some number with which packing fails (when aspect ratio fails to be maintained). Issue seems to be specific to ETC textures. Issue does not happen when target platform is set to standalone, iOS. Issue persists when application is built.

Error:
Assertion failed: Assertion failed on expression: 'expectedSize + offset == length || (expectedSize < 64 && length == 64 + offset)'