Thanks for the report! As of today morning, I cannot reproduce the issue. Maybe it was transient?

I was just able to replicate via https://test.wikipedia.org/wiki/Special:RecentChanges

After a long wait, the page loads with no results and the following message:

This search has timed out. You may wish to try different search parameters.

Interestingly, test2-wiki sees to be not affected: https://test2.wikipedia.org/wiki/Special:RecentChanges

What are the differences between test-wiki and test2-wiki?

In T362722#9725173, @Michael wrote:

Interestingly, test2-wiki sees to be not affected: https://test2.wikipedia.org/wiki/Special:RecentChanges

What are the differences between test-wiki and test2-wiki?

Yes, the issue seems to be happening only on testwiki so far. I checked wikis in group 1 wmf.1 - the issue is not present. Still, the issue is easily reproducible on testwiki. I'll check group 2.

In T362722#9725173, @Michael wrote:

What are the differences between test-wiki and test2-wiki?

Configuration (test2wiki has some features that testwiki does not have, such as FlaggedRevs) and version (testwiki is the first wiki where new MW version is deployed to, but test2wiki is a group1 wiki, meaning it is deployed on Wednesday, together with eg. Wikidata or Commons, so it runs older code on certain days).

Checked group 2 - no issue. The logstash also doesn't report the issue anywhere except testwiki wmf.1