The strangest thing suddenly occurred; one product, at least only one that I'm aware of, is not appearing when using the site's search bar. The product is marked available and can be found on various collection pages. However, when it's searched for in the site's search bar, the product does not appear. Instead, only the products that mention the missing-search product are shown.
I have done the following to troubleshoot the issue:
Deactivate product - save - reactivate product - save
Remove from online store - save - add to online store - save
I tested another Shopify site using the same query parameters (just swapped out the keywords to match the other product) and the results came as expected. There
If you're using an app for search, I would contact the app developers.
If your search is built into the theme, I would contact the theme developers.
In both cases they'll know the algorithm they're using and can probably solve this pretty quickly.
One other thing to try, if you're using an app and there's an "index" feature in the app settings, try running that. It's possible that the product is not in the search index.