Many requests such as this one https://query.wikidata.org/sparql?query=SELECT%20%3Fid%7B%3Fid%20wdt%3AP2600%20%22xxx%22%7D%20LIMIT%201%231337 times out or returns 429 (tried in PAWS shell).
Email sent to Wikidata Users list:
We are aware of an ongoing issue with WDQS that begun around 1500 UTC today. To stabilize the service, we have introduced drastic measures including banning cloud provider IPs and certain user agents. Unfortunately, this will likely affect legitimate users of the service. We are currently working on less disruptive measures and will update https://phabricator.wikimedia.org/T324346 when we have more information to share. Thanks for your patience, and we sincerely apologize for the inconvenience.
Follow-up email sent to Wikidata Users list:
At this point, we believe we have mitigated the stability issues, and legitimate users should be able to access the WDQS service once again. If you are still having issues, please respond here or on the Phabricator ticket linked below. Thanks once again for your patience and have a great weekend!