Map viewer symbology not showing in web app builder

[Psoralea]

Hi - I have published a Feature layer to AGOL with no errors  or warnings.  It shows up looking good in Map Viewer but the styles are not retained in Map viewer classic.  When I go to create a Web App it seems to use the Map Viewer Classic symbology, which is not what I want. 

Is it possible to get the Map Viewer symbology used in the Web App? 

I am pretty sure that the Map Viewer symbology has displayed in my Web Apps before, and I cant see why AGOL is defaulting to the terrible symbology of  shown in Map Viewer Classic?

Map viewer symbology

Map Viewer Classic symbology

[ChristopherCounsell]

Going to guess that you are using Vector symbols:

Vector symbols are only supported in some ArcGIS apps. Instead of the vector symbols you apply to a map, a default symbol is applied when the map is used in apps that don't yet support these symbols. To determine whether vector symbols are currently supported in a specific ArcGIS app, refer to the app documentation.

https://doc.arcgis.com/en/arcgis-online/create-maps/use-style-options-mv.htm

Or possibly some other newer functionality introduced in the Map Viewer that is only supported in it or apps that use the new API.

Map Viewer Classic, Web AppBuilder, 'classic' apps and configurable app templates use the JavaScript API 3.x.

Map Viewer and new app designers such as Experience Builder, ArcGIS Dashboards, ArcGIS Story Maps, and Instant Apps are designed to use the 4.x API.

If you use mix the 'classic' or new map viewer with another app style, you may find issues like what you are seeing.

I would recommend using Map Viewer and the new apps that leverage the 4.x API. Don't use classic viewer or apps that have retired. You are going to have a bad time and face more incompatibility issues. Only people that have existing apps, or some specific need to be on a classic map/app, should be on them. There are not many reasons for this.

Some discussion on this here for the most common Web AppBuilder:

https://www.esri.com/arcgis-blog/products/web-appbuilder/announcements/arcgis-web-appbuilder-roadmap...

[ConorFlynn]

My solution for a line layer:  use Basic Line > Basic Shapes (Classic Symbols).  Vector symbols don't work. 

BUT I can only do this if I select Types (Unique symbols).  Location (single symbol) only gives Vector line choice even if I choose Vector line > Basic shapes (Classic Symbols).