If a Feature Service is published with the symbology set via an Arcade expression, the feature class's subtype info is not carried into the service definition. This means subtyped data has to be published with simple symbology classes which isn't ideal for displaying all types of data. I assume this has to do with an ancient limitation of the Server platform where subtypes and symbol classes have to be tethered somehow, either way this restriction should be lifted to support more expressive symbols in web GIS workflows.
(Apologies if there's a better hub for this idea, figure the same fix should work for both portal types)
