Just a thought. I have a Montana 610 and a 64s and was running OSM maps from a popular site. I had a problem where both GPSs would shut down /turn the screen off randomly while navigating. Over a period of 12 months I literally tried everything including getting a replacement Montana from Garmin and the problem remained. I then tried Garmin maps and have not had a problem since. Just wondering if there is some incompatibility between Garmin and OSM.