I got a message from my phone saying it was out of space trying to do an iCloud backup. The Aura app was set to back up but was occupying 3.4 GB of data storage.
I seems that if you download a transcoded recording and then that recording is later deleted on the Aura box then the recording is deleted on the Aura app but the transcoded data remains in the app storage.
At this point there is no way to delete the orphaned data except by deleting the whole app.
There are multiple issues here:
1. Deleting a recording on the Aura box should delete downloaded recordings on IOS, that is the job of the Aura app itself
2. Downloading recording should not be flagged for backup. Sky Go excluded these.