I have a couple of layers in a map in Field Maps and one of them when I select a feature gives me the ability to edit and modify all of the existing attributes, but when I am not in the editting option it only shows "Edited by" instead of showing me the full list of attribute fields. I have all the pop ups enabled to show the fields in Visualization so not sure whats going on with this. Other layers in the same map show the attributes when not editing.
Have you opened the map in Map Viewer (not visualization tab of data details) and configured the popups there?
If so, does it behave the same? (i.e. not showing attributes)
R_