Update Jan 17: Ok
now APK uploads to sandbox should be successful. (We triple checked this time.) Again, if you're still having issues, please provide that information below.
Update Jan 16: Our previous update was an error. We found that the first APK upload was successful but all subsequent uploads failed. The investigation continues. Thank you for your patience.
Update Jan 15: Uploading APKs to sandbox should be functioning as normally now. If you are still having issues, please respond here with relevant additional information.
We're aware of the issue that developers are having when uploading their APKs to sandbox. This is currently being investigated.
Clover is monitoring the situation and will keep you updated.