SignalR ends up flooding my application pool (causing blocking)

I've been having this problem for quite some time, where somehow the state of one of my SignalR clients (or many of them?) Enters this behavior when switching to longPolling and then fills my application pool completely. There will be many reconnections and polling start / stop requests. It looks something like one of these two screenshots:

Ultimately my whole web server gets blocked as the application pool fills up.

What can cause these scenarios? Why does it fall back to longPolling, and why does it end up flooding the server?