504 response code when uploading archives

Trying to release a build to staging and it's failing to upload:

• What went wrong:
  Execution failed for task ':Simperium:uploadArchives'.
  > Could not publish configuration 'archives'
  > Error deploying artifact 'com.simperium.android:simperium:aar': Error deploying artifact: Failed to transfer file: https://oss.sonatype.org/service/local/staging/deploy/maven2/com/simperium/android/simperium/0.6.0/simperium-0.6.0.aar. Return code is: 504 {/code}