Configuring Blazor Server to only use WebSockets

I’m trying to configure my Blazor Server app to only use WebSockets as the transport so as to not need to enable sticky sessions on our load balancer. I have tried the following:

_Host.cshtml

	<script src="_framework/blazor.server.js" autostart="false"></script>
	<script>
		Blazor.start({
			configureSignalR: function (builder) {
				builder.withUrl("/_blazor", {
					skipNegotiation: true,
					transport: 1
				});
			}
		});
	</script>

Startup.cs

app.UseEndpoints(endpoints =>
{
	endpoints.MapBlazorHub(options => options.Transports = HttpTransportType.WebSockets);
	endpoints.MapFallbackToPage("/_Host");
});

That configuration results in errors:

blazor.server.js:1 WebSocket connection to 'wss://domain.com/_blazor' failed: 
blazor.server.js:1 [2021-04-19T20:04:18.010Z] Error: Failed to start the connection: Error: There was an error with the transport.
blazor.server.js:21 [2021-04-19T20:04:18.011Z] Error: Error: There was an error with the transport.
blazor.server.js:1 Uncaught (in promise) Error: Cannot send data if the connection is not in the 'Connected' State.

Is there a different configuration I need to be doing for Blazor Server to only use WebSockets?