First off, this is the faulty turnout. Testing revealed that both of the inbuilt jumpers from the stock rails to the short rails that exit the frogs had failed, leaving the short rails unpowered.
As one of the stock rails on the turnout to the immediate left (in the photo) of this turnout received power from this short rail, it too was unpowered, leaving me with a section of rail approximately 20cm (8") long that was 'dead'. The problem was exacerbated by the fact that these turnouts were laid when I was still operating on DC/cab-control, so I had used insulating rail joiners to connect them to the adjacent track blocks.
The yellow wires in the above photo power the frogs through slide switches.
I reinstalled the turnouts using metal rail joiners instead of plastic joiners.
I was surprised to find that this turnout had failed as it has been in place for several years. Hopefully, with the changes I've made, I will have no further problems with them. However, it does make me think that I should replace the rest of the insulating rail joiners, and add power feeders to the remaining turnouts that I have at Davis and Wynnewood, before I start building scenery. Hmmmm............