[LW] [LW11] Axiom - Fuel Remaining shows ---, why?

[DaveInDevon]

This is a new Axiom 9 installation and the estimated Fuel Remianing just shows Dashes.
I have set the Total Fuel Capacity = 640 Litres
I have set the Fuel Manager to use the Fuel Rate from PGN127489 (using the Detect Fuel Messages)
I have set All Tanks Full (even though they aren't)
So having used a very small amount of fuel I would expect "Est Fuel Remaining" to be 640 or very close. Instead it just shows the dashes as though it hasn't been populated, so I'm puzzled.
Engines are 2xKAMD300 each with a Yacht Devices Engine Gateway (YDES04) onto the N2K network to which the Axiom is connected. There is also A Yacht Devices Voyage Recorder (YDVR04) which shows that the engine is sending fuel flow rate data & the Axiom does show some fuel used - see attachments.
Hopefully I haven't missed a configuration step out
Axiom is running LH 3.11.42
Engine Gateways are at latest release