UWorld writes "Contrary to popular belief, patients may be quite distressed by their symptoms. An indifferent attitude toward severe symptoms (ie, la belle indifférence) occurs with equal frequency in both conversion and true neurological disorders and therefore is not a reliable indicator of conversion disorder"
UpToDate also writes that la belle indifference "has no validity in discriminating functional neurological symptom disorder from recognizable neurologic disease...In our experience, la belle indifference often indicates that patients are trying to appear brave or cheerful in the presence of actual distress (to avoid receiving a psychiatric diagnosis such as depression)."
It does not serve patients any good, and rather risks harm, to continue teaching that la belle indifference may indicate conversion disorder.
Source: UWorld - Step 2 3719