It is easy to forget to update <solr_home>/conf/shared.properties for the port.
It is easy to change the port at start up using the "-p" option.
These should be linked.
SOLR 6 sets the system property jetty.port at start up
1) Remove the default config entry for solr.port in sharded.properties
2) If solr.port is present we still use it - its main use is for a proxy
3) If solr.port is absent, use jetty.port