I just thought I would share this in case anybody else experienced the problem.
- i changed the default port for the SSH plugin
- i installed the shellinabox plugin
everytime i entered the username in the shellinabox either as terminal, or as webclient, the session closed straight away.
i saw this thread when trying to get to the bottom of it.
https://github.com/shellinabox/shellinabox/issues/88
As soon as i changed the SSH plugin port back to 22, shellinabox was working again.
I guess the shellinabox plugin should be modified to be aware of the port that the SSH plugin is using.