tmux no server running on /tmp/tmux-*/default - Windows msys2 terminal
tmux no server running on /tmp/tmux-*/default - Windows msys2 terminal windows
windows
Sending SIGUSR1 to tmux is only useful if the tmux server is already running but something has deleted its socket from /tmp. Are you sure this is the case?
If there is no tmux server running, you just need to start a new one with "tmux new".