Due to a defect introduced in 3.1.4 the nodetool utility no longer recognises the --port option.
A side effect of this issue is that the Opscenter diagnostic tool will produce invalid output similar to the following:
/usr/bin/nodetool --host=127.0.0.1 --port=7199 info
exit status: 1
usage: java org.apache.cassandra.tools.NodeCmd --host <arg> <command>
Unrecognized command: 7199
To work around this issue you can replace the existing nodetool in your installation with the following fixed version.
The issue is fixed in 3.1.5 and later releases.