HLS Offline Error Domain=CoreMediaErrorDomain Code=-16247 on DRM-protected streams

Hello, I keep getting this kind of errors (specifically 16247) when trying to download DRM-protected HLS content, would anyone have a clue about the reason why ?

Error Domain=CoreMediaErrorDomain Code=-16247 "(null)" UserInfo={_NSURLErrorRelatedURLSessionTaskErrorKey=("BackgroundAVAssetDownloadTask <AE4BADBD-135D-44FB-AFC9-36A231AB1901>

Thanks

Sylvain