Error reported on SPARQL query

[jrh...@thematix.com]

The following query works once, but if I try to re-execute the query, I get an error message.

Here's the query:

SELECT DISTINCT ?cls ?pred ?par WHERE {

{?cls ?pred ?bn1 . ?bn1 rdf:rest*/rdf:first ?par .

FILTER ((?pred = owl:intersectionOf || ?pred = owl:unionOf || ?pred=owl:oneOf)

) } UNION

{?cls ?pred ?par . ?par rdf:type owl:Class

FILTER (( ?pred = owl:complementOf || ?pred = rdfs:subClassOf)

) } UNION

{?cls ?pr ?pred ; owl:onProperty ?op. OPTIONAL{?op rdfs:domain ?par} FILTER(?pred = owl:Restriction)}

            FILTER ( ?cls=<_:bnode_5f216aed_42e5_4515_811f_5473cabb63d0_851> ) }

Here's the error message

Error!

java.lang.IllegalStateException: This scan does not provide an ordered output and cannot skip through solutions:  IndexScan(order=SPOC, first=_:bnode_5f216aed_42e5_4515_811f_5473cabb63d0_851, second=http://www.w3.org/2002/07/owl#onProperty, third=Var(6))   sort type: SortType[0]

If I stop the server and restart it, this query works once and produces the correct result. The second time I execute the query, and every time thereafter, I get the error.

In this instance, only the third branch of the UNION is bound with ?cls to the bnode, ?pred to owl:Restriction, and ?par to fibo-fnd-aap-agt:AutonomousAgent.

Let me know if you need any more information to diagnose this problem.