Getting session URI from shapshot:

https://firebase.google.com/docs/reference/android/com/google/firebase/storage/UploadTask.TaskSnapshot.html#public-uri-getuploadsessionuri-

and using the snapshot URI for uploading:

https://firebase.google.com/docs/reference/android/com/google/firebase/storage/StorageReference#public-uploadtask-putfile-uri-uri,-storagemetadata-metadata,-uri-existinguploaduri

This would help uploading a file from where it left off when the app was killed