It is not advised to reindex StackState unless this was explicitly recommended by StackState support.
For search and querying purposes, StackState builds an index out of data in the graph database. It is possible to initiate a rebuild of this index from StackState's graph database. Note that under normal circumstances you will never need to do this.
Make sure that StackState is not running with the following command: systemctl stop stackstate
Make sure that StackGraph is running with the following command: systemctl start stackgraph