Not clear what thread is waiting for

I'm trying to figure out why an http request from my browser to my .net mvc application takes so long. Using DotTrace I've figured out that it's because it's in a waiting state for very long.

It's unclear however how to continue with this because there is not a lot of information as you can see in the screenshot. For example, what does "No Activating Thread" mean in this context?

What should I do to try and fix this?