Results disapper on exact prefix

We have a strange behaviour with our Magento search bar. One particular exact prefix (composed of three words) for a product name returns 0 results. If the last word is truncated, or a typo is present, 11 results are returned.
I have replicated the API calls with curl, with the same results, and noticed that the returned json has the “query” field composed of a single space in the case of exact prefix, while it’s just two words in the case of a typo present.

How can these be possible?

Thank you.