The Untoward Incident Review Group (UIRG) ruled that France did not follow head injury assessment (HIA) protocols.
France replacement Uini Atonio went off for an HIA in the 81st minute, with tight-head Rabah Slimani returning.
However, UIRG said "there was no clear evidence that there was any intent to obtain a competitive advantage".
The match at the Stade de France ended with an extraordinary 20 minutes of added time, during which France were camped on the Wales try line as the home side sought a winning score.
Referee Wayne Barnes allowed France to replace Atonio with Slimani, who had earlier been replaced, with the France team doctor insisting Atonio needed an HIA.
Slimani's return came during a series of scrums on the Wales line, and France finally won in the 100th minute when Damien Chouly drove over from close range.
After the defeat, Wales interim head coach Rob Howley said: "There is evidence to suggest the integrity of the game has been brought into disrepute."
France have been reprimanded for an incident involving a change of props during the conclusion to March's Six Nations 20-18 win over Wales in Paris.