Thanks for capturing and sending these!  I can see the issue in the SQL now.  Below is a plain text, formatted copy of the pxSQLStatementPost for the initial and drilldown runs:

Initial:

SELECT
    Count(CASE WHEN ( PYRESOLVEDTIMESTAMP <= PYSLADEADLINE ) THEN 1 ELSE NULL END) AS "pySummaryCount(1)",
    Count(CASE WHEN ( PYRESOLVEDTIMESTAMP > PYSLADEADLINE ) THEN 1 ELSE NULL END)) AS "pySummaryCount(2)",
    TYPE AS "Type",
    WORKBASKET AS "WorkBasket",
    CLOSEDISPOSITION AS "CloseDisposition"
FROM
    hnb_casemgmt_work
WHERE
    ( pxObjClass LIKE ? ) AND
    (
	    ( TYPE = ? OR TYPE = ? ) AND
        ( PYSTATUSWORK LIKE ? ) AND
        CLOSEDISPOSITION IS NOT NULL
    )
GROUP BY TYPE, WORKBASKET, CLOSEDISPOSITION
ORDER BY TYPE, WORKBASKET, CLOSEDISPOSITION

Drilldown:

SELECT
	Count(CASE WHEN ( PYRESOLVEDTIMESTAMP <= PYSLADEADLINE ) THEN 1 ELSE NULL END) AS "pySummaryCount(1)",
	Count(CASE WHEN ( PYRESOLVEDTIMESTAMP > PYSLADEADLINE ) THEN 1 ELSE NULL END)) AS "pySummaryCount(2)",
	TYPE AS "Type",
	WORKBASKET AS "WorkBasket",
	CLOSEDISPOSITION AS "CloseDisposition"
FROM
	hnb_casemgmt_work
WHERE
	( pxObjClass LIKE ? ) AND
	(
		( TYPE = ? OR TYPE = ? ) AND
		( PYSTATUSWORK LIKE ? ) AND
		CLOSEDISPOSITION IS NOT NULL AND
		(
		    ( TRND1ATRND1 ) OR
		    ( TRND2ATRND2 )
		)
	)
GROUP BY TYPE, WORKBASKET, CLOSEDISPOSITION
ORDER BY TYPE, WORKBASKET, CLOSEDISPOSITION

As you can see, the WHERE clause was modified to include the condition ( TRND1ATRND1 ) OR ( TRND2ATRND2 ).  This isn't exactly the final SQL statement, as the prepared values have not been inserted, but this may be the issue, considering the error message complains about an invalid relational operator.

Unfortunately I cannot help you, but someone within Pega who has familiarity with the SQL generation for Summary Views might be able to help.  Since this looks like it may be a product defect, you may choose to open a Support Request with us for further assistance.