The 'Total Distance Driven' at the top of the Driver's log is either the ECM recorded distance driven (if there was an ECM connection) or the GPS distance driven, but not a combination of the two. So it won't display the total distance driven by the Driver for the day if there is an ECM connectivity issue.

Remember that the Driver log is a legal doc displaying gov't required information rather than your business requirements (i.e. wanting to know the total distance driven regardless of the method of capturing it). So, if you want to see the combined total distance driven you'll want to be accessing the the Shift Report.
Note: if you click the Driver's Name on the Driver's log it will take you directly there :-)