All,
We are actively working on a fix for this issue. It's a priority for us to address. The underlying issue is related to ArcGIS Server map services where the field alias does not match the field name.
In the meantime, there are a couple of workarounds that you can consider to help?
1) Republish the service such that the field aliases match the field names
OR
2) When adding the layer to the map, us the full URL to the layer ID, instead of just to the root of the map server.
i.e. add the layer with http://sampleserver6.arcgisonline.com/arcgis/rest/services/CommercialDamageAssessment/MapServer/0 , and not via the Root URL "http://sampleserver6.arcgisonline.com/arcgis/rest/services/CommercialDamageAssessment/MapServer
Question for you all - what version of ArcGIS Server is hosting the services that are giving you trouble? The fix for services on pre and post 10.5 is different, hence the question.
Thank you - we are working on getting a resolution to this issue as soon as we can!
Heather