The last few weeks I have been experiencing extremely poor ssh performance. It appears that BT has started to shape or disrupt SSH connections.
The ssh session experience drop outs, disconnections, freezing, stuttering. All of this intermittent and point towards purposeful disruption of service by BT technicians.
I don't pay extra for BT business fiber so that I have a poor service.
I don't think it's an SSH issue. SSH either works or not. I haven't seen any intermittent issues yet. Try to do a continuous ping test to this node and see if there a few or lots of time outs.