Sometimes the connection is cut for some reason, and may leave behind an ssh process hogging a forwarded port, preventing me from connecting again. The solution is simple - kill that process.
But in order to kill the rogue process I need to find its process id. Now how do I do that? Easy - by using netstat to look up which process is listening to one of the forwarded ports:
netstat -lnpA inet | grep -e 590.