Operation returned an invalid status code 'Forbidden'/'NotFound'

Sayali-MSFT Apologies for the delayed response, I was on vacation for the last week. I'm not sure what the repro steps are for this issue as it happens intermittently and looking at the telemetry there doesn't seem to be any common ground or any cases where it happens 100% of the time.

I've included the area of code where I think the error originates from below. Like I mentioned in my original post, we are using the WaterfallDialog approach with this bot and this is one of the steps, the error seems to be thrown when moving away from this step to the next.

private async Task<DialogTurnResult> PromptStepAsync(WaterfallStepContext stepContext, CancellationToken cancellationToken)
{
	try
	{
		UserProfile Profile = await this._stateAccessor.GetAsync(stepContext.Context, () => new UserProfile());

		if (String.IsNullOrWhiteSpace(stepContext.Context.Activity.Text))
		{
			if (!String.IsNullOrWhiteSpace(Profile.CachedMessage))
			{
				stepContext.Context.Activity.Text = Profile.CachedMessage;
				Profile.CachedMessage = String.Empty;
			}
		}

		return await stepContext.BeginDialogAsync(nameof(OAuthPrompt), null, cancellationToken);
	}
	catch (Exception exc)
	{
		Dictionary<String, String> Properties = new Dictionary<String, String>();
		Properties.Add("Class", "MainDialog");
		Properties.Add("Method", "PromptStepAsync");

		AppInsightsHelper.LogException(exc, Properties, stepContext.Context);

		await stepContext.Context.SendActivityAsync(BotResponse.ErrorMessage_GenericErrorResponse);
		return await stepContext.EndDialogAsync(cancellationToken: cancellationToken);
	}
}