well, most easily visible in LAX-DOH: no other airports involved, but actual and potential are far apart.
I actually found one like that as well. EWR-CAG in GW2.
CAG does not overlap with anything, and my flight is the only flight to the US. Yet, the actual cargo demand is only 3,290 out of potential of 11,300.
My flight has been up for about a year, more than enough time to shift the demand.
So looks like there is indeed a bug here. I have no idea how this one differs from other airport pairs where the demand does shift correctly....