We identified an issue with the Android build queue and resolved it soon after receiving this message. Please try again. Apologies for any inconvenience.
I have the same problem, but with iOS. It only occurs when I add the Firebase plugin cordova-plugin-firebasex. To make it work I had to downgrade the plugin to an old version.
We’re currently running a beta that should make this build quicker. If you can share you email address I can add you to the beta and you can use the “beta servers” checkbox on our upload page.