The last I checked, Uber miles should almost always be more than what the Uber statement shows. 

You should to ask the client if he has adequate records that document his miles.  If he does, then prepare the tax return.

Uber miles are the paid miles. It doesn't include the "off the clock" miles that were required. You can't get to the airport to pick up a fare without incurring "off the clock" miles. What you want is proof of Business miles, not just proof of paid miles.