I have a some named fields where the field alias name is Shape.STLength. I've checked the FC in ArcCatalog and I don't see anything fields where the alias name is totally different then the field name. Why is a different field alias Shape.ST appearing in the service and can I fix this by adding a new field to the FC?
James,
That looks like a publishing error. I would first try and re-publish the service. If that is still an issue then delete the service and re-publish.
I needed to go back into the mxd and reset the field order in the layer properties then republish the service.
https://community.esri.com/thread/182363-why-cant-i-continue-configuring-the-pop-ups-on-my-agol-map