When upgrading to DB2 iSeries 7.1, Remarks for tables and columns are not properly shown anymore. The reason for this is that there has been some internal changes in the DB server or the JTOpen JDBC driver. 

The workaround is to add a driver property for the actual database connection in DbVisualizer: 

metadata source = 0

Driver properties are edited in the Properties tab for your DB2 iSeries connection, by selecting the Driver Properties category. In the list to the right locate or add the metadata source property and set the value to 0

For a full list of driver properties for the JTOpen driver check this.