I’ve completed with success the return of Razor special event

Losing the BMW you earned is not a normal part of the game as far as I know.

You might want to look at the topics about lost data.

@rabiadeer Completing the "Return of Razor" special event is supposed to give you the BMW M4 F82 (Razor) permanently. You're not supposed to return the BMW M4 F82 (Razor) back to Officer Rivera if you won the race against Razor.

If you lost the BMW M4 F82 (Razor) after completing the "Return of Razor" special event, then it's impossible to get it back as the special event is over almost a week ago.