Stalled SSH connections

I spent some time adjusting my SSH configuration because I often get stalled connections to my servers but I never got that fixed until recently, when I started looking in my firewall settings on the pfSense.

After changing the Firewall Optimization Settings within System → Advanced → Firewall & NAT to Conservative I had no more of these hangs of my SSH sessions.

I use the ControlMaster setting in my SSH configuration so the stalled connections have to be killed with something like

$ ssh -O exit {short hostname}

every time – which is annoying.