After Updating Android Studio 3.1 Get Error while Release Signed APK

Check your PNG images, corrupted maybe or not real png (jpeg for example)

You can get the list of unreal PNGs by typing following command in android terminal

find . -type f -name "*.png" | xargs -L 1 -I{} file  -I {} | grep -v 'image/png; charset=binary$'

i saw somewher someone add this code to build.gradle i tried it and its solve my problem

lintOptions {

    checkReleaseBuilds false

    // Or, if you prefer, you can continue to check for errors in release 
    //builds,
    // but continue the build even when errors are found:

    abortOnError false

}

buildTypes {
    release {
        aaptOptions.cruncherEnabled = false
        aaptOptions.useNewCruncher = false
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 
        'proguard-rules.pro'
    }
}