Straight lines appear in the track log

If your track log seems to contain straight lines at various points, instead of accurately following the course you took, then the only explanation is that the GPS was unable to get a position fix for some period during the trip.

The app will record track points continuously while travelling, but if the satellite signal is lost for any period of time, and then regained, then the app can only draw a straight line between the point where the satellite signal was lost, and where it was regained.