GPS lon/lat stucking issue

[jmk7791]

We are testing with EVKF9P.
When we run the code roslaunch ublox_gps ublox_device.launch and check out lon/lat by rostopic echo /ublox/fix, a lon/lat stucking issue occurs.

When the position covariance value gets really low (lower than 1.0), sometimes lon/lat and position covariance are fixed to certain values, and do not change even if we move with the GPS.

Is there anyone who suffered from same issue? or how can we deal with it/what will be the reason?