What does it mean? What do I do about it?
The default value of 50 does not adequately cover application usage of indexes.
Increase -indexrangesize. Suggested settings are in $PROTOP/dbname.range.pf
The suggested settings give you a choice. You can monitor just application tables and indexes or you can expand the range to include system tables and indexes. There can be a surprising amount of activity in the system tables and it may be enlightening to monitor those as well.