When cell connectivity is lost, Navistream is 'offline' and no longer able to update Fleet Tracking with the latest location information until the unit gets back into cell service. During any cell disconnection time all information is collected and stored on the tablet (inc. location information, Duty Statuses, etc.) and when cell connectivity is restored all the information is uploaded for you to be able to see on the web portal - mynavistream.com. In other words, the tablet always is up-to-date for the Driver whether in cell coverage or not, and the web portal is updated based on whether the tablet has cell connectivity or not.
So, on Fleet Tracking you'll see the last time the location updated in the left panel and when you hover over the vehicle icon. When a tablet goes out of cell service you'll notice that the last known location stops updating. After 30 min. of no location updates the vehicle icon will turn yellow. After 1h it will turn red. After 2h it will turn grey.