I was able to determine the issue here. It seems that the Integration Field Override Service Name is NOT required, nor are the list of integration fields on the connector configuration page. These are listed under the “Filter Settings” section and I think are actually intended to be used as filter criteria (although the documentation isn’t very clear in the connector guide). Anyway after removing these two settings from the configuration, but leaving the Integration System ID, any integration field listed on the schema does come back now.