Hi Jaco,
please make sure that you have installed this plugin:
cordova-android-support-gradle-release
Please use the version 2.0.1 of that plugin, there were some changes in Android recently that break the build system.
Also, please make sure to use the version 7.1.2 for the Android platform.
So I recommend you to run:
cordova platform remove android
cordova plugin remove cordova-android-support-gradle-release
cordova platform add android@7.1.2
cordova plugin add cordova-android-support-gradle-release@2.0.1
Cheers,
Dani