Hello,
Since I upgraded from ArcGIS Enterprise 11.0 to ArcGIS Enterprise 11.1, many of my ArcGIS Field maps are broken.

In Field Maps, I have the following error:
[LOADING] Layer (Arrêts d'urgence AUG) failed to load with error: Error Domain=com.esri.arcgis.runtime.error Code=2 "Invalid argument" UserInfo={NSLocalizedFailureReason=UTF8 contains invalid characters, NSLocalizedDescription=Invalid argument., Additional Message=UTF8 contains invalid characters}
When debugging with Fiddler, I noticed that the following request:
https://agsserver.company.com/arcgis/rest/services/MyServer/FeatureServer/3?f=json&returnAdvancedSymbols=false
returns badly encoded accent letters (I am French):

The funny thing is that if I remove 'returnAdvancedSymbols' parameter, it is clean:

I made a test with an ArcGIS Server 11.0 and even if 'returnAdvancedSymbols' parameter is specified, the response is properly encoded.
I also made a test to bypass WebAdaptor 11.1 thinking it might be the culprit but I am getting the same poorly encoded reply from ArcGIS Server.
Thanks !
NB: The error is from IOS FieldMaps. On android it does not crash but I have this weird � character instead