SDE feature class fields that are originally checked-off when published in ArcMap, and checked-on and republished, are put at the end of the attribute table in the ArcGIS Online Map Viewer.
Last Published: May 16, 2019ArcGIS for Server
Bug ID Number
May 8, 2015
August 21, 2020
ArcGIS for Server
After review by the development team, it has been determined that this issue is related to a known limitation with the software that lies outside of Esri's control. The issue's Additional Information section may contain further explanation.
The existing popupInfo did not have these fields and so it adds these newly added layer fields at the end of the list and unchecked. Users can reorder and hide fields for the pop-up, so we thought that would be the best. Removing the popupInfo and enabling pop-ups again makes it different.
Share the map service as a new item in ArcGIS Online, and point the web map to the new item. The bug is no longer present.