I get the same with version mediastreamvalidator: Version 1.4 (417.2-190530) and SAMPLE-AES encrypted content. On the other hand, the technote https://developer.apple.com/library/archive/technotes/tn2454/_index.html says that encrypted playlists are not supported:
"The mediastreamvalidator only supports regular HLS m3u8 playlists so you will need to run it against the unencrypted variant of your content instead of your encrypted variant."
so I think the result is consistent with that sentence.