Why is RedisSearch missing documents in results when querying with a prefix on a tag field?

In Redis, I have a full-text index on JSON documents with a field called lemma_exact. It is tied to an array of strings on the underlying JSON document.

I can find a certain article using the index with the following query:

(@lemma_exact:{viking})

This returns the article I am looking for. However, if I use this query:

(@lemma_exact:{*ing})

I get articles where the indexed field contains a value that ends in -ing. This is what I want. However, it does not include all articles — notably, as in this example, not the one where the field is "viking".

What may be going wrong here?

Things I've already checked:

• Stop words are disabled on the index (set to an empty list).
• The JSON document had no errors during indexing.
• The range I passed to FT.SEARCH was large enough to contain all results.
• I increased the timeout on FT.SEARCH to 10 000, but this did not change anything.

Timeout was my first thought here too, so you're thinking about it correctly. You could always set the ON_TIMEOUT behavior to FAIL to confirm that the timeout isn't being hit. But 10 seconds is forever in Redis terms, so I doubt that it will be.

However, it might be worth playing with the MAXPREFIXEXPANSIONS setting. Increasing it is a performance tradeoff, but I've seen these sorts of issues before when a prefix or suffix is particularly common. And -ing is certainly common.