Esri Map component (esriMapMarkerField, plugin) — Search box failing with "At least one source is required" despite valid OAuth credentials

We're integrating the Esri Map component (esriMapMarkerField) from Esri plugin with Appian, connected via an OAuth 2.0 "Other application" (client credentials) connected system pointing to ArcGIS Online. The map itself renders correctly — basemaps, drawing tools, and geometry capture all work as expected. However, the built-in address Search box fails, throwing these console errors from esri.widgets.Search.SearchViewModel:

suggest:no-sources-defined — "At least one source is required."
search:no-sources-defined — "At least one source is required."

Troubleshooting so far:

• Confirmed our ArcGIS org has the World Geocoding Service properly assigned under Utility Services.
• Confirmed our OAuth Client ID/Secret generate valid tokens (tested independently via Postman, including successful calls to findAddressCandidates).
• Initially found the widget's internal sharing/rest/portals/self call (used to auto-discover the org's default geocode source) was returning 498 Invalid Token, despite the token working for other Esri endpoints.
• Marking the OAuth app item as "Authoritative" in ArcGIS Online and updating the connected system to use that app's credentials resolved the 498 on portals/self — it now returns 200 OK, confirmed via browser dev tools on the live Appian call.
• Despite portals/self now succeeding, the Search box is still not reliably returning address suggestions/results when typing in the map — we're still validating whether sources are correctly populated end-to-end.

Has anyone else run into this specific combination — client_credentials/application tokens failing on portals/self until the app is marked Authoritative — with this plugin? And separately, is there a known additional step needed after portals/self succeeds for the Search widget to actually populate usable geocode sources and return results? Any insight into whether this is a plugin-side limitation vs. something further in ArcGIS org config would be appreciated.