I notice that, under load, my ASP.NET Core website generates request telemetry with duplicate Operation IDs.

It appears that HostingDiagnosticListener isn't written with multiple simultaneous requests in mind.
In particular, this.client.Context.Operation.Id gets overwritten by each new request (line 44)
(Also beginRequestTimestamp)

Rather that setting the Operation ID in the client's context (which is like setting it globally), I believe it should be set in the RequestTelemetry object that is added to HttpContext.Features
One would think that the timestamp could also be recorded in the RequestTelemetry object (indeed it already has fields for recording start time, so it's odd that it's not initialized here)