Spotify is designed so that when a publisher needs to update the content of an episode without actually publishing a new one, this will update any ‘available offline’ (downloaded) episodes.
The number of episodes the listeners of any particular show have made available offline are unknown to us, until a redirect is placed. When you redirect the ‘enclosure URL’ (where the file is served from your host) is updated and the spike of all your listener's apps re-downloading episodes occurs.
This the Spotify post-redirect spike. They are aware of this behaviour.
To help with this, Omny can bypass ad delivery for the duration of the initial spike caused by migration for episodes published more than 30 days ago.
Publishers can expect a download spike from Spotify, variable in size depending on listener behaviour (how many have your episodes downloaded), when migrating a show, or changing or adding a prefix tracking URL.