Again, US DVD/Blu-ray players and displays are known to have issues with 25 or 50 field/frame content (SD or HD) - they’re generally not made with anything other than NTSC/film specs in mind (whereas European players have been NTSC ready since the DVD era).

The sources of the fan-collected Alien materials are a combination of (true) NTSC and PAL frame rates, e.g.

Shock and Awe (UK broadcast documentary - 50i)
James Cameron: A Director and His Work (US tape source - 59.94i)
Giger’s Alien (shot on 16mm film - 23.976fps)

There’s no one disc medium that will support all of these formats and play anywhere in the world - there has to be a compromise somewhere along the line.