That’s a bug we identified recently in the verification path (when you run select * or when you select an unindexed field) with query string queries - https://issues.couchbase.com/browse/MB-44356 (this will be addressed in the upcoming release).
Try the following queries and you should see consistent results …
SELECT *
FROM search AS a
WHERE sub_type="market-explorer"
AND SEARCH(a,"app_provider_name: dark" )
SELECT *
FROM search AS a
WHERE sub_type="market-explorer"
AND SEARCH(a,{ "fields": ["*"], "query": { "field": "app_provider_name", "match":"dark" }})