MediaPlayerApp: TLS errors and heavy lagging with auto-loaded video URL

To reproduce, run one of the two mediaplayer app examples:

qtdoc/examples/demos/mediaplayer/

qtmultimedia/examples/multimedia/video/mediaplayer/

The app will auto-play this video-URL:

https://download.qt.io/learning/videos/media-player-example/Qt_LogoMergeEffect.mp4

Now jump around in the movie and observe heavy lagging accompanied by outputs like these:

[tls @ 0x6000002ac300] Unable to negotiate TLS/SSL session: -9806
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x14477e890] stream 0, offset 0x182741: partial file 

[tls @ 0x600000c1c200] IO Error: -9806
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x12cf0d7d0] stream 0, offset 0x338dc8: partial file

Big hint: When opening the same URL in a browser I get redirected to this URL instead:
https://mirrors.dotsrc.org/qtproject/learning/videos/media-player-example/Qt_LogoMergeEffect.mp4
...and using this mirror directly as a URL in mediaplayer works fine.