The unitLabel attribute for the fitField element of the fitContributions XML is not optional, it must be included. Therefore, I set this to a null string ID, e.g.:
<string id="lEconomyUnits"></string>
However, although this looks fine on the Garmin Connect Mobile Android app after uploading an activity, it appears in the Stats section of the activity summary on the Garmin Connect web site like this:
107 [2aadad94-c678-4dff-ab1d-2438f0b996edlEconomyUnits]
Obviously I just want it to show the value, '107'.
When you hover over the record graph it appears in this fashion, with the app ID and string ID, but in the list of splits (laps), the column of lap values looks fine (no label is shown).