To reproduce:
1. Open attached project "OSXIconGlitch.zip"
2. Build for MacOS standalone
3. Right-click on the built project > Show Package Contents > Contents > Resources > right-click on PlayerIcon.icns

Expected result: all icons are the correct size
Actual result: 128x128 icon is corrupted

Reproduced on:
2017.1.4f1 2017.2.3f1 2017.3.2f1 2017.4.4f1 2018.1.2f1 2018.2.0b5 2018.3.0a1

Notes:
Seems to be working fine on win10 machine.
Changing the size of the icon on MacOS to 128x128 on the desktop is also working just fine. The corruption seems to be only visible in the Resources folder in PlayerIcon.icns file.