Possible causes
Missing assortment, weak product data, spelling, customer language, filters or index problems can all lead to a no-result.
Glossary
Zero-result rate
The zero-result rate is the proportion of searches that do not produce results.
Do not blindly lower
More results are only better when they are relevant; a forced match can actually take the customer further from the right product.
Prioritizing
Combine volume, buying intent and commercial relevance to determine which zero-results deserve attention first.
After the fix
In addition to the rate, also check CTR, follow-up steps and conversion to see if the solution really helps.