Jim, 
Feel free to contact us, you may simply need to perform a GPS Factory Reset to grab a new GPS Almanac.  Also, you might try to swap the two units.  The antenna could have been shadowed by a door pillar or wind more that the other.   Also, was there a phone or Bluetooth closer to the 720, than the 700.  Just looking for some sources of GPS interference.   Please feel free to contact us for some troubleshooting on this.