I'm wondering if this is a bug or if it's just not supported.
In my web map I configured the pop up to show a field from a related table (The relationship is M to 1, i.e. many geometry features are related to 1 table row). For this case, the statistical operator doesn't matter (sum, ave, min, max) as there is only one related record.
The web map popup looks as expected, but in the web based ops dashboard the value is empty.
Thanks for your assistance.