In this final image I turned up the DC voltage to 1.3V and we can now see the diodes beginning to allow current to flow. The Fluke is measuring 0.03A or three hundredths of an amp at 1.3V across the diodes.
This GI is doing what it should and will block dangerous DC galvanic current.
One last very important point and that is the name of these tells the story GALVANIC ISOLATOR. Galvanic isolators are only capable of blocking voltages created by connecting dissimilar metals together in an electrolyte (the Ocean).
Galvanic isolators DO NOT BLOCK STRAY CURRENT FROM DC LEAKS THAT EXCEED 1.2V.....!!
With that in mind this is why you would never, ever see my own vessel plugged into a marina relying solely on a GI. If you desire true isolation then an ISOLATION TRANSFORMER is necessary, or unplug...
Hope this helps!!