The incorrect application of rules was caused by human error, according to the governing body of Formula 1.
The race director acted in good faith during the controversial finale which saw Max Verstappen win the title from Lewis Hamilton.
F1 race control has been restructured after Masi was removed from his post.
The result and the World Championship were determined by the report.
The report confirms that Max Verstappen was the F1 world champion in 2021.
A number of key errors were made which led to the single final racing lap on which the world title changed hands from Lewis Hamilton to Verstappen.
It ended.
The race director "called the safety car back into the pit lane without it having completed an additional lap as required by the Formula 1 sporting regulations".
There "could be different interpretations" of the safety-car rules in the sporting regulations.
The decisions made by Masi "likely took into account previous discussions that made clear the F1 stakeholders' (FIA, F1, teams and drivers) preference to end races under green-flag racing conditions, rather than behind a safety car, when safe to do so.
Human error led to the fact that not all cars were allowed to un-lap themselves. From now on, the communication as to the cars that must un-lap themselves will be automated.
Direct communications to Masi from both Mercedes and Red Bull teams "had a negative impact on the smooth running of the final laps because they were distracting when the race director needed to focus on making difficult and time-pressured decisions"
Due to the fact that manual interventions carry a higher risk of human error, software has been developed that will automate the communication of the list of cars that must un-lap themselves.
There are a number of measures taken to avoid the same errors happening again. These include:
The establishment of a remote operations centre at the FIA headquarters in Geneva to assist race control, in the manner of football's video assistant referee (VAR).
An extended team in race control to run trackside operations.
Direct communications from teams to the race director "should be removed to protect the race director from any pressure and allow him to make decisions peacefully".
Un-lapping procedures behind the safety car will be reassessed.
A new race-management team of two race directors - Niels Wittich and Eduardo Freitas - acting alternately and assisted by former deputy race director Herbie Blash, who has returned to FIA employment after retiring in 2016, to assist in race control as permanent senior adviser.
What was the pre-report reaction?
Before the report was published on Saturday, a number of team bosses and drivers said that it was time for F1 to move on.
Wolff said earlier on Saturday that they need to turn the page. Nobody wants to continue the discussion about Abu Dhabi.
Hamilton, who lost a possible eighth world title in Abu Dhabi, said on Friday that it was important that the sport was transparent.
Hamilton said that he was looking forward to seeing the report and that it would show that the sport is transparent and will make improvements moving forward.