This was a bug in TerraSync version 5.8 where the software would crash when trying to save a feature while a data file was open as a background file. upgrading to 5.81 or later will fix the issue.
Visit the rental story map to get all the basics on collecting data, navigating, and transferring data using TerraSync and Pathfinder Office. https://storymaps.arcgis.com/stories/6400358a8a3b4fa99a350b119cd903f2
When using a MN County Coordinate System in TerraSync to test the accuracy via data feature or waypoint be sure that your coordinate system units are set to 'US Survey Feet' instead of 'Feet'