The Ubisoft forums have word for The Crew players who have noticed some of their stats were lost, saying they are aware of the issue, and working on a fix, and reassure players that that no major data like Cars, Money, or Levels were lost (thanks Videogamer). They say that as of now the servers are no longer resetting these stats, but they may be continuing to display incorrectly for the moment. Here's word:

Lately, some players have been encountering an issue where some game statistics where lost.

Our team has been looking into it and was able to identify the issue. What was happening is that the server was sometimes unable to load your stats and erasing them.
With today’s Patch, the server will no longer be erasing your statistics however it might still be displaying the wrong stats.

In short, your stats are no longer reset but they might not be properly displayed.

Be sure that the team will be fixing this last issue for good in a future patch, until then, if you want to see your stats you can log off and log back into the game a couple of times and you should see them properly.

We thank you for your patience and understanding.
The Crew Team.