FileBot

I tried to download subtitles for a show right after its release and several days following. However, no subtitles were found using hash match (and name search resulted in the 409 error that I often get).

I then cleared the cache: "filebot -clear-cache" and subtitles were then found by hash!

Is it necessary to clear the cache before searching for subtitles?
What is the purpose of the cache?

Caching reduces load on OpenSubtitles if you repeatedly send the same search requests. Data is cached for a maximum of 48 hours, so waiting 48 hours is equivalent to clearing the cache.

So if you continuously search for subtitles, you can only get new results every 2 days. And if you only perform one search every 2 days you will always get new results.