alan Sch, if I understand you right, then you use report template "Geofence" and Minimum Speed and Maximum Speed settings.
filtration works the following way: we choose intervals of geofence visiting. After that, we see if the interval corresponds to filters. As for speed filter, then we see if the speed in the interval includes speed in the filter. E.g. we have an interval with speed in messages 5, 11, 19, 60, 80 km/h. We set the filter from 10 to 20. We see that we have values in the interval that corresponds to filter (11 and 19). Then the whole interval is correct.
You may use the option in filtration setting "Retrieve intervals", then you'll get the interval with cut values (in our example the final interval will be 11,19 with this option).
But I recommend solving the root of the problem - invalid speed value. You may look for the device settings or at least set a maximum speed in messages validity filtration.
Ex-Business Analyst, Gurtam