Recently, WDQS servers started to get a lot of failed requests from www.wikidata.org for recentchanges API:
Aug 24 17:01:37 wdqs1003 wdqs-updater[26210]: Caused by: org.apache.http.NoHttpResponseException: www.wikidata.org:443 failed to respond
This slows down the update process and leads to WDQS lags. Also may indicate something is wrong with Wikidata servers, as this hasn't happened before.