For the past couple of days this has got significantly worse. Running the same script as before, wdqs10* are returning the expected 1360 results¹, but wdqs20* have degraded even more:

http://tinyurl.com/y8l62tav is another example: this is currently only returning 40 rows for me, when it should be returning over 50.
A DESCRIBE on one of the missing results (Q48622226-55106E3A-52C1-4927-B004-8C97A6D25365) shows only the p:P39, with no qualifiers at all.

@Smalyshev, not sure if this is related, but a query of DESCRIBE <http://www.wikidata.org/entity/statement/Q54356755-13A869AC-9E98-4D75-9809-613418E23405> is currently only returning the pq:P768 and pq:P4100, and is missing the ps:P39 and pq:P2937 (and thus not being returned in queries for all members) — see some discussion at https://twitter.com/tmtm/status/1039048340812517377