Browser Instrumentation not working

We’ve recently deployed to a new environment using Net Core and found that our Browser monitoring no longer works.
We’ve read the documentation and understand that auto-instrumentation no longer works (https://docs.newrelic.com/docs/agents/net-agent/additional-installation/new-relic-browser-net-agent).
However we have been using the manual instrumentation method as detailed on that page; adding the call to @Html.Raw(NewRelic.Api.Agent.NewRelic.GetBrowserTimingHeader()) in our Razor template.
When checking this on the deployed site it simply outputs the HTML comment " <!-- New Relic Header -->" and doesn’t output the monitoring JS.
The code runs via IIS on a Windows server with the 64bit APM Agent installed. (8.17.438.0)

What have we missed? We’ve enabled it as far as we can tell?
Is there a bug we’ve missed?

Many thanks,

Mike

@mikesmith -

The message " <!-- New Relic Header -->" means the .NET agent itself is not active.

The default implementation (when the .NET agent is not active) for NewRelic.Api.Agent.NewRelic.GetBrowserTimingHeader() outputs that string. When the agent is active it provides an implementation that actually inserts the browser agent into the page.

It sounds like you went from a .NET framework app to a .NET core app and I think the issue is that agent 8.17 doesn’t monitor .NET Core apps out of the box.

Can you try upgrading the agent to the latest? It’ll monitor both .NET framework and .NET Core (asp.net core) apps.

Also see this post for more info.