Steps to replicate the issue (include links if applicable):

See T376440 (it was closed again and I was asked to instead create a new issue).

The deepcategory search does show partial results now so the other issue seemed done. However, apparently it can often fail. The example category did show many results sometimes but sometimes no results again. I thought it was a temporary problem because when I checked the search again, it did show results again but now it failed again to show results

• Open/search for deepcategory:"Manufacturing by product"(link) in the Wikimedia Commons search

What happens?:
It shows no results and the error

Deep category search timed out. Most likely the category has too many subcategories

In case it works for you at the time when you look at this issue, here is a screenshot:

What should have happened instead?:
It should always show those partial results (as it does only sometimes).

Here's how it looks like when it works:

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):