IARSpider

A follow-up on this: After fixing the hash, the resource pack was still not downloaded from the server. It turned out that if there is a resource pack file inside world folder (in this case iarspider.new.year.2020.2021/resource.zip), then the server will silently ignore resource-pack property and send a special kind of link to the resource pack (level://iarspider.new.year.2020.2021/resources.zip). I guess this is how resource packs are handled in singleplayer worlds.