I found this reference to hidden fields (see #2 in the screen capture above). It is from over 2 years ago. I have published several dozen layers from Desktop ArcMap to AGOL to make available to Open Data. Upon further review, I have found that hiding fields does not always work... sometimes it does, other times, not. In fact, I found at least one example within one published layer where some of the hidden fields remained hidden and at least one did not. All fields that show in AGOL are passed to Open Data; my problem is the initial publishing from ArcMap to AGOL. As far as I know, any field name aliases are correctly published.
Any insight to solve this issue would be appreciated.