I said this in another thread.

Power saving settings. When it's not set to "normal" it will shut the GPS or app down until you pull it back up again. Now and then mine gets reset to "Smart" for some reason and that's when I get the straight line GPS error because it shuts down and doesn't record until I check to see if it's recording or use the phone for some other purpose. Drives me crazy when it gets set off of "Normal".