Amazon has not publicly explained the mechanism behind that change. That leaves a fairly important boundary around the story. We can describe what reached users, but not whether the underlying mistake involved scheduling, availability rules, publishing permissions or something else inside Prime Video's systems.
The customer-facing release looked complete
According to The Verge, Dominic Preston verified access to the full 95-minute runtime. The Prime Video page also carried normal title metadata including cast information, a thumbnail and a plot description.
That separates the incident from a simple metadata typo. The visible problem was not merely that Mutiny appeared in search a couple of days too soon; the feature itself was playable.
The title was later switched to unavailable. No public technical postmortem has followed, and Amazon had not provided The Verge with an explanation when the incident was reported.
There is no evidence for a deliberate early launch
The movie is produced by MadRiver Pictures and Punch Palace Productions, while Lionsgate is distributing it in the United States. Its official US marketing still points to an August 21 theatrical release. The early streaming window was removed rather than announced as a change of plan.
France had already opened the film in cinemas on August 19 through SND, so describing this as a leak before the movie reached any theater would be inaccurate. The mismatch was between Prime Video US and the planned American theatrical window.
What remains unknown
Nothing currently published identifies the internal control that failed or the person, system or process responsible. The existence of a fully populated page tells us that the video and customer-facing metadata were simultaneously available to the service. It does not tell us why playback was permitted.
Mutiny, directed by Jean-François Richet and starring Jason Statham, remains scheduled to open in US theaters on August 21. As of August 20, Amazon has not issued a public explanation for the early Prime Video availability.