Please see these ArcGIS Help links:
An overview of spatial indexes in the geodatabase
http://desktop.arcgis.com/en/arcmap/latest/manage-data/geodatabases/an-overview-of-spatial-indexes-in-the-geodatabase.htm
Rebuild a spatial index
http://desktop.arcgis.com/en/arcmap/latest/manage-data/geodatabases/modifying-a-spatial-index.htm
Common errors that may occur during editing
http://desktop.arcgis.com/en/arcmap/latest/manage-data/editing-fundamentals/common-errors-that-may-occur-during-editing.htm