Recently when I enabled Proguard in my program like the following:

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release {
    minifyEnabled true
    shrinkResources true
    proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}

I faced the problem that it tooks like for ever for the process of transformClassesAndResourcesWithProguardForRelease. This problem happens when you have multiple libraries need to be Proguard/Dexguard. Add the line multiDexEnabled true in to your gradle defaultConfig will fix this problem.