There are a few reasons why sometimes you might see limited (or no) search results within Keyword Scout.
First, remember that when you run a reverse ASIN search, the tool only returns the keywords that place that ASIN among the top 100 search results. This means that, even if an ASIN has 120 keywords, if the ASIN is not found in the top 100 results for any of them, then those keywords won't be displayed in the reverse ASIN lookup results.
Also, when looking for specific keywords, you might not see any, or get limited results in cases when those terms are relatively new or not as popular as other keywords.
And keep in mind that results are tied to a specific marketplace. Searching for keywords in the Amazon US store is going to get you more results than searching in smaller-scale marketplaces such as Mexico or Germany.
Generally speaking, when using the keyword lookup function, the tool does a broad match on all keywords that share a certain number of ASINs with the original keyword entered, so it will give you more results than when running a reverse ASIN search. Once you get those results, you can use the filters to drill down and identify high-performing organic and sponsored keywords as well as keywords that your competitors are targeting.
Also, when you run a reverse ASIN search in Keyword Scout, even if the product is a best-seller, it is possible that the search won't return any results. This happens when the ASIN is a variant. While the "parent group" (the combination of all child ASINs) may be globally indexed for hundreds of keywords, the single child ASIN may return little to no results in KWS. There's a workaround for this though! If you enable the "Include all variants" option, your results will include keywords from all child ASINS. You can move the slider to the on position to activate (green) or deactivate (grey) this option. If you chose not to enable this feature, your results will only include keywords for that specific ASIN.
Finally, keep in mind that Keyword Scout updates its data a few times per week. You might see more results in a few days.