Discord actually does send GUILD_CREATE lazily after connecting for bots, this is documented clearly in their own docs and I can recreate that behaviour with a raw WebSocket connection currently. If you previously relied on behaviour where it does not, that must be something your bot library has masked for you on Discord previously, which is possible to do if it doesn't let you use the bot until all guilds have arrived asynchronously after READY, so this requires no changes to Fluxer source code, but either changes to the library you use, or your expectations of said library.
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Comment by Hampus
GUILD_CREATElazily after connecting for bots, this is documented clearly in their own docs and I can recreate that behaviour with a raw WebSocket connection currently. If you previously relied on behaviour where it does not, that must be something your bot library has masked for you on Discord previously, which is possible to do if it doesn't let you use the bot until all guilds have arrived asynchronously afterREADY, so this requires no changes to Fluxer source code, but either changes to the library you use, or your expectations of said library.