SSH connections dropping out

I have a host which is running on a Raspberry Pi behind a firewall. If I try to make a connection to it, the connection initialises, then when I copy the IP address and port details and try to log on it gets as far as letting me log on and run a couple of commands, then disconnects the session.
The same thing happens if I try a VNC session, I can log on to the session and see the interface, but then I get disconnected before I have chance to do anything.

In this case the connections started working again without issue. There is a potential that something happened on the host network since there was no changes on the Remote.It side. This could be when the wifi router NAT tables or memory has issues which is somewhat common on residential grade routers. A reboot of the router usually solves this issue.