After converting data, the data segments not used in the FHIR results will be underlined in the data pane. If you don't need this feature, you can deselect the option called Enable Unused Segments Diagnostic in Preferences > Settings > Workspace > Extensions > FHIR Converter or add a setting "microsoft.health.fhir.converter.enableUnusedSegmentsDiagnostic": false in the workspace setting file.