Changing the default shell in SmarTTY from
sh seems to solve the problem. This is possibly a bad design of SmarTTY: it should by default respect to remote user setting, instead of calling
bash regardless. Some platform, a router in OP’s case, doesn’t have enough space to provide a Bash. On those platforms, user's log-in shell is
sh, and when the user SSH into it, a decent SSH client (such as OpenSSH) would ask the daemon to start a log-in shell.
Note: this behavior is SSH specific. It doesn’t matter you’re on Windows or Linux.