1651117 - BI4 Explorer when clicking Explore more.. getting error: Failed to retrieve list of values.

When Exploring an Information Space and at the bottom of the facet clicking Explore more... getting following error: "Failed to retrieve list of values. Failed to retrieve the record cell item."

In the Exploration Server log we see error:

java.lang.NullPointerException: while trying to invoke the method org.apache.lucene.index.IndexReader.numDocs() of an object loaded from field com.businessobjects.datadiscovery.dataprovider.lucene.index.member.LuceneAttributeMemberRegistry.attributeIndexReader of an object loaded from local variable 'this'

SAP BusinessObjects Explorer 4.0 SP02 and later.

Failed to retrieve list of values, Explorer facet LOV, list of values explorer, record cell item, failed record cell item, explore more... error , KBA , BI-RA-EXP , Obsolete: Polestar, Explorer , Problem