We are having some issues with 2 of the Wikidata Query Service
servers. So far, the issue looks like data corruption, probably
related to an issue in Blazegraph itself (the database engine behind
Wikidata Query Service). The issue prevents updates to the data, but
reads are unaffected as far as we can tell.
The 2 affected servers are part of the internal WDQS cluster, so the
public wdqs endpoint  is not affected. Data is lagging on the
internal eqiad endpoint, so Mediawiki functionalities that use WDQS
are at the moment not seeing the latest updates to Wikidata.
We are reaching out to the Blazegraph team via Github  and via
private contacts that we have. We hope to identify the root cause of
the issue so that we can fix it for good, but this looks like a hard
problem. Failing that, we will reimport the full data set.
You can follow the upstream issue on Github  and on Phabricator on
our side .
Sorry for the inconvenience and thank you for your patience!
Operations Engineer, Search Platform
UTC+1 / CET