Hi Ashley... I´m trying just now, and sharing my results
1) Now I can build, but only using export> unsigned APK. This creates a file called myproject.android.release.apk. A few days ago, by the same way, it was built a file called myproject.android.debug.apk
2) I can´t build using export > Signed release APK, I create a new keystore and it fail again. I share the fail message.
Regards