Understanding Calculation of Travel in the Salesforce Field Service Gantt

For Field Service Lightning to calculate travel, the start and end points must be geocoded. If there is not calculated travel for the first and last travel (from home base and back to home base), that means the resource home base is not geocoded.  

The resource home base is the address of their Service Territory Member records, so make sure a well-formatted address is used that can be geocoded. Use the address on their Service territory if the resource home base is defined to be the office.

If there is travel between appointments where travel is not calculated, it means that one of the Service Appointments was not geocoded. Again, check the address of these appointment.

Add the 'data integration' related list (fka 'clean rules') to see the state of the geocoding.

The Salesforce Field Service Managed Package has a trigger in which changing the latitude and longitude will calculate new travel times.  However, if a change of the latitude/longitude is done using the platform's geocoding/data integration rules, and the bypass trigger checkbox is true, the managed package travel calculation trigger will not trigger.