Some emote sets are empty

Hi crasty! You are not missing anything. This has been reported multiple times on the emote endpoints announcement and twitchdev issues repo on github.
I am not a Twitch employee, but given lots of testing of mine and others I can safely say these emote sets contain emotes that are “tied to user’s account”, e.g. hype train emotes, kpop event emotes, pride emotes, 2020 emotes, etc.
Even if you were to get the emote objects for these sets, and a user has the set in the (GLOBAL)USERSTATE message, not all emotes from that set might be available for the user to use.
There’s still Get Authenticated User Emotes endpoint in Kraken API, which does return these emotesets with all emotes that are available to the user (not necessarily all emotes from the emoteset). You can use that for the time being if you’re working with the emotes of your user, but keep in mind that Twitch wants to axe whole Kraken namespace by the end of February 2022.
There’s no migration path for that Kraken endpoint which I personally find stupid as there’s literally no way to get information about these emotesets. There is a Uservoice ticket requesting a Helix equivalent of mentioned Kraken endpoint. Upvote it and maybe Twitch will notice us and realize that that endpoint like the Kraken one is actually critical for developers to have in the new API if the old one is being decomissioned.
I am only sharing my experience with the topic and can’t help you, but I hope this helps understand the issue.