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The problem is with one of your config. Post debug.log to know which

You know reobfJar doesn't prevent you from decompiling your mod and it doesn't completely obfuscate your mod, right? It only reobfuscates what you use that is obfuscated in Minecraft.

Advancements are just json files in data/MODID/advancements in your resources. Check out vanilla advancements to see how they work things. Also, the minecraft wiki page on the advancements json format is helpful: https://minecraft.gamepedia.com/Advancements/JSON_format Hope this helps! Try making some simple ones, and if you have trouble, post logs/code/json (or logs, and a link to a github would be better), and I'm sure someone will give you a hand.