I have seen the Local Business Center reports lag behind by two days or so at times. When this happens, the graphs show zero traffic for those two days, and then in another day or so when their traffic number-crunching catches up, the graphs suddenly bounce up to showing normal traffic patterns.
Also, if you've been penalized in Google Maps, your listing might abruptly drop down to zero traffic levels. You should do some typical searches where your listing was appearing, and see if it's still showing up in the search results.
If you think you have been penalized, you should revise your LBC business profile to match up with their quality guidelines. Google LBC recently revised their quality guidelines, becoming slightly more conservative in what is and is not allowed.
My listing has been up for a few months and I've been waiting for stats to display ever since the announcement that they were available...but nothing showing yet, though my listing is still displaying prominently so no penalties here.