I SSH into a Ubuntu computer from a Windows computer using PuTTY. I run tmux (actually byobu which runs tmux underneath) and at a shell inside tmux I find that the left and right arrow keys do not work. They are actually detected as shift+left and shift+right arrow keys inside tmux.
This problem has been discussed here. One of the suggested solutions was to add
set enable-keypad on to
~/.inputrc. That did not seem to work for me.
However, the above bug report also mentioned that this was a bug in tmux and it was fixed in tmux 2.4. So, I used this tmux PPA and updated the tmux 2.1 shipping in Ubuntu 16.04 to a tmux 2.6. The arrow key problem disappeared.