question

Ussually if this sort of thing happens its because the GPS unit you are using has lost its accuracy at that time and thus the system thinks you have moved. has the GPS antenna got good reception and a good view of the sky.

Further to Paul, In this case, the VGX and VRM are only acting on the information that they are receiving from your GPS device.

If you can't increase the accuracy of the GPS unit and it's calibrations or antenna. A possible work around would be to increase the size of the geofence (using the data you already have) to find out how far it 'roams' and keep the alerts to only outside that perimeter.

Not sure if you got to the bottom of this, and I realise this was over 12mths ago - but this may be for the benefit of others as well...

You can add the GPS Widget on the VRM portal, and from there Download the GPS tracks, they download in KML format, which can be imported into Google Earth.

https://support.google.com/earth/answer/7365595?co=GENIE.Platform%3DDesktop&hl=en

You can see here after 1 day of data from my BU-353-S4 GPS which is on my Venus inside my Broadcast Van - so it's inside a bit of a faraday cage and I know it will never be holely accurate.

However this gives me enough data to set an accurate enough Geo fence with a large enough radius to remove the False positives. After all - if for instance someone were to steel the van, whether it has moved 2 houses down or 3 streets away would really make little difference and only be the difference of probably less than a minute.

For you - Further to Paul B's query about it having clear view of the sky - GPS suffers a multitude of errors, one for instance is known as Multi-path effect - where particularly in your case things like Masts, or metal bulkheads if antenna inside, could potentially either block the path of 1 or more sats, or Cause reflective signals at specific times and cause huge triangulation differences - so not only a clear view of the sky, but you need to make sure the GPS antenna is clear in all azimuth not just to the zenith.

Even Receiver noise could be caused by someone else in the marina operating RF equipment, Generators, Electrical tools, etc.

I suppose all in all - you also probably shouldn't rule out the Marina operator taking her out for a spin Ferris Bueller Style! :)