The newer versions of Ionic/Cordova/Android use a different build location for android

[walljm]

I'm on Ionic 4. I had to change line 35 of minifier.js to this:

_this.platformPaths.push(path.join(_this.basePath, platform,'app', 'src', 'main', 'assets', 'www'));

to get it working.

[Leffe108]

upstream cordova-uglify solved it this way:
rossmartin/cordova-uglify@eca7302

Which is similar to your solution, but should be backward compatible as well.