Two filter conditions in a row produce empty result (sometimes)
Works:
select ?s ?difficulty ?topic ?level ?label ?descr where
?s <rdf:type> <edu:LearningGoalType> ?t
& ?s <edu:hasDifficulty> ?difficulty ?t2
& ?s <edu:hasGoalTopic> ?topic ?t3
& ?s <edu:hasLevel> ?level ?_
& ?s <edu:label> ?label ?_
& ?s <edu:description> ?descr ?_
filter HasLanguageTag ?descr "en" & HasLanguageTag ?label "en"
Breaks: (but works with one filter, and not with the same applied twice!)
select distinct ?s ?topic ?label ?descr where
?s <rdf:type> <edu:AchievementType> ?t
& ?s <edu:hasAchievementTopic> ?topic ?_
& ?s <edu:label> ?label ?_
& ?s <edu:description> ?descr ?_
filter HasLanguageTag ?label "en" & HasLanguageTag ?descr "en"