I have come across various issues regarding popups working correctly in Pro but when published to Enterprise 10.7.1, the popup configuration does not come through.
I tested using custom popups. I used 3 different objects to create the popup, first being a text with a custom expression, second I turned on a few fields, third was a text object with more custom expressions.
Works great in Pro.

When published to Portal, only the 1st object (text values) gets passed through for the feature service. With the image service, nothing passes through.
feature service
image service
Is this a known limitation with Portal?
I have been told that there is a bug logged:
BUG-000108454 : A customized pop-up in ArcGIS Pro fails to show the field value in the pop-up pane after publishing a hosted feature service to ArcGIS Online
Though this references ArcGIS Online and hosted feature service (I'm using referenced data from postgres db) it does sound like a similar issue.
I just want it confirmed that others are experiencing the same issue?