Tmux key bindings not working

I fixed this by deleting my ~/.tmux.conf and using tmux kill-server

Depending on your situation, "kill-server" might be overkill.

For me, the non working keys is fixed by just detaching the client that stopped working, and re attaching to it; in a different terminal:

tmux detach-client -s mysession
tmux attach-session -t mysession