Why Can't an Encrypted HLS Video Be Played After Being Transcoded for the Second Time?

One possible cause is key caching on the HLS key server. With this setup, Key Management Service (KMS) can cache retrieved keys locally. This allows it to return keys directly for subsequent requests from playback clients, without having to fetch them from VOD every time. Consequently, when the decryption key changes after re-transcoding, the cache on the key server must be cleared to ensure it retrieves and serves the new key.