terminal scrollbar not working

problem: terminal scrollbar sometimes stops working.

below solution taken from askubuntu.com

The behaviour you describe sounds like your terminal was stuck in the full screen "cursor addressing" mode used by tools like less and vi.

The mode can become stuck if those programs do not exit cleanly. For instance, if you kill -9 them, or are running them through an ssh session that disconnects. You can exit this terminal mode by running the following command:

try

$ tput rmcup

or

$ tput reset