How to diagnose a SSH remote port forward not working
Solution 1:
You need GatewayPorts yes in sshd_config to be able to access it from outside.
Solution 2:
When you specify 2255:localhost:2255 fills the missing hostname in front as a localhost. This will really bind only to localhost address (loopback). If you want to use it also "from outside", you need to use the server IP for the remote port forwarding, such as example.com:2255:localhost:2255.