I was under the impression that the attribute editing popup in Field Maps was determined by the Pop-up configuration. With the new update, the Pop-up is reflecting a configuration set in ArcPro and saved as a web map to AGOL. The Pop-up is honoring the configuration set but the order of the attributes for editing does not. Please see the attached photos displaying the difference.
Attribute Order when editing.
I haven't been able to test this but if I set the pop-up configuration in Pro prior to saving it as a Web Map, does the pop-up configuration dictate the initial order of the form?