I can't craft either of them ( JEI shows no recipe and the default recipe doesn't work), I think they were supposed to be unlocked when I completed the "Gather Ores" quest, seeing as it has "More Recipes Unlocked" as a reward. This means I'm stuck at the "Smelting" quest, I've crafted every other item necessary

I'm still not quite sure why gamestages seem to malfunction so frequently.. but the easiest way to fix this would be to enter the command /gamestage add @p tinkers

Wow, thanks for the ridiculously fast reply, it worked!

It happened again with the scarab crafting recipe, additional info: On a server owned by me, this time noticed that when I claim the recipe the console logs "Unknown command"
(Also what's the name of this gamestage?)

This gamestage is just called energy i.e. /gamestage add @p energy. I'm not sure why this bug is happening assuming you aren't running a cracked client, but it seems to happen to 1 in every few hundred people.

There is one more gamestage in the second to last chapter if this comes up again. The command is /gamestage add @p netherstar

Actually. there is yet another game stage (4 in total, all mentioned now in this thread).
/gamestage add @p mummy in chapter 4

My account is premium (if we still call it that) and my server is set to online mode, also, I'm guessing the server itself counts as 1 out of those 100 people, considering another player on my team reported the same. I'm hoping this will be fixed eventually, until then I may just add my own reward for the quest and a shop at spawn that trades it for the command.
Thank you for the temp fix, please open this thread again if you ever find out how to fix it more permanently

I figured it out. I went into editing mode to see the quest rewards to see that it's the commands you gave me (for some reason I thought it would be some other command), and it has a / at the start, as it turns out, /say hi returns "Unknown Command" while say hi makes the [Server] say "hi" (I thought / also worked in servers).
I removed the / from all the gamestage quests, this should only work for servers, and thus the original version should only fail for certain servers.
Thanks for the help and for pointing me in the right direction

Have this fixed with a pull request