I wonder if someone did something; max lag seems to have returned to normal levels since around 10:00 UTC.

The issue has got progressively worse over the past several hours, and max lag is now at around 40 minutes:

@Epidosis Hi, what makes you say that QS 3.0 respects maxlag? I checked the source code and see no reference to maxlag.

@lerickson Hi, I noticed the following three deleted items are being returned by WDQS:
https://www.wikidata.org/wiki/Q136696641
https://www.wikidata.org/wiki/Q136766770
https://www.wikidata.org/wiki/Q138507916

I think it would help if the persistent ID is not solely limited to numeric values.
Although many websites use numeric values as their persistent IDs, others might use an alphanumeric string, a GUID or so on.
For instance, YouTube channel IDs look like UCBR8-60-B28hp2BmDPdntcQ (whereas the human-readable handle looks like @YouTube).