Adding a mod with more advancements after editing advancements crashes the game

[SupersuMC]

Describe the Bug

After editing the advancements in-world, deleting all worlds causes the game to crash when the new world creation screen comes up.

Reproduction Steps

1. Create a world
2. Edit the advancements
3. Add a mod that adds more advancements
4. The create world screen crashes, rendering play impossible, and current worlds can't be opened or re-created.

Expected Result

Being able to create a new world, re-create an existing world, and open a world.

Screenshots and Videos

No response

Game Version

1.21.1

Mod Version

6.2.4

Mod Loader

NeoForge

Loader Version

21.1.249

Other Mods / Modpack

• 3d-Skin-Layers [1.11.2] by tr7zw
• AI-Improvements [0.5.3] by BuiltBrokenModding
• All The Leaks [1.1.12+1.21.1-neoforge] by Uncandango
• AmbientEnvironment [18.0.0.2] by Jaredlll08
• Aquarius Libs [1.2.0] by aquarius_playz
• Architectury [13.0.11] by shedaniel
• Armor Stand Poses [1.3.0] by legopitstop
• Atmosfera [1.0.2] by Leclowndu93150
• BE Style Wither [1.8.0] by MORIMORI0317
• Backport [1.0.9+mc1.21.1] by BloodyDreames
• Backported [1.2.0] by WooleyMoley
• BadOptimizations [2.4.1] by Thosea
• Balm [21.0.65] by BlayTheNinth
• Bedrock Impaling [1.0.0] by AverageGameUser, MCreator
• Bedrock Jockey [1.0.0] by AvatarKage
• Bedrock Stuff [18.1] by Pinguinmike
• Bedrockoid [0.1.5] by SashaKYotoz
• Brick Pyramids Infdev [1.0.0] by SmartStreamLabs
• CME Suck My Duck [1.2.0] by Liu Dongyu
• Chunk Activity Tracker [1.0.1] by Toni
• Classic Structures [2.3] by Necromancerkai
• Cloth Config v15 API [15.0.140] by shedaniel
• Collective [8.39] by Rick South
• Configurable [3.5.2] by Bawnorton
• Configured [2.6.3] by MrCrayfish
• Configured Defaults [21.1.3] by Fuzs
• Controlling [19.0.5] by Jaredlll08
• Copper Age Backport [0.1.4] by Smallinger
• Copper Age Backport Durability Fix [0.1.0] by iamthemcmaster
• Copper Age Backport Registry Compat [1.0.0] by Hearthbound Horizons
• Crash Assistant [1.11.12] by KostromDan
• Deer Mod [0.6.1+1.21.1] by ArisuwuMei
• Default Options [21.1.8] by BlayTheNinth
• Desert Update [1.2.1-1.21.1] by PixelDarks, Danyless, NicoloMario10
• Discontinued Features [1.0.0] by matt, MCreator
• Disrobe Sounds [1.0.0+1.21.1+neoforge] by ZipeStudio
• Does It Tick? [1.1.4] by Toni
• Dolphin Fix [1.1.0] by Tazgirl
• Dynamic FPS [3.11.4] by juliand665 & LostLuma
• Education Edition Reforged [1.0.4] by KakuzatouRemi, MCreator
• Entity Model Features [3.3.5] by Traben
• Entity Texture Features [7.2.1] by Traben
• EntityCulling [1.10.5] by tr7zw
• EntityJS [1.5.0] by Liopyu,Too Much Mail
• Factory API [2.2.9] by Wilyicaro
• FancyMenu [3.9.12] by Keksuccino
• Farlands Reborn [2.0.0] by AdyTech99!
• Featurify [2.0.13] by Faboslav
• Ferrite Core [7.0.3] by malte0811
• Friendlist & P2P Play Backport [1.1.0] by juanmuscaria
• Friends&Foes [4.0.27] by Faboslav
• Fzzy Config [0.7.6+1.21+neoforge] by fzzyhmstrs
• GeckoLib 4 [4.9.2] by Gecko, Eliot, AzureDoom, DerToaster, Tslat, Witixin
• Hey Wiki [1.7.7+1.21.1] by Minecraft Wiki
• ImmediatelyFast [1.6.13+1.21.1] by RK_01
• Immersive Optimization [0.2.0] by Luke100000
• JEI Info Remover [1.0.0]
• Jockey API [1.0.0] by AvatarKage
• Just Enough Items [19.53.0.426] by mezz
• Just Enough Resources [1.6.0.17] by way2muchnoise
• Konkrete [1.9.9] by Keksuccino
• Koopa's Critters [1.2] by Redkoopa & Coda
• Kotlin for Forge [8335665]
• KubeJS [2101.7.2-build.377] by latvian.dev
• KubeJS Offline [1.21-5.2.3] by ILIKEPIEFOO2
• KubeJS Recipe Designer [1.1.0] by LucasGamerKongen
• KubeJS Studio [1.1.0] by TysonTheEmber
• Legacy Mechanics [1.1.0] by Pigzone00
• Legacy Nether: Extended [2.0.1] by Pigzone00
• Legacy4J [1.8.6-lts] by Wilyicaro
• Lithium [0.15.4+mc1.21.1] by 2No2Name, JellySquid
• Load My F***ing Tags [1.1.1+1.21.9] by Blodhgarm
• MapDistanceFix [1.1.2+mc1.21-1.21.11] by mrerenk
• Melody [1.0.10] by Keksuccino
• Minecart Backport [1.1.0] by N0t_UN_Owen/NotUnaNancyOwen
• Mixin Trace Reforged [1.0.0] by Toni, comp500, MCTeamPotato
• Mob Control [2.0.1-beta-2] by Ohayden
• Mob Sound Variantions [2.5]
• Mod Credits Reborn [0.1.5] by {author}
• Mod Menu (NeoForge Edition) [1.0.2] by Raguto, foxy, Prospector, haykam821, TerraformersMC
• Modern Director [6772488]
• ModernFix [5.27.24+mc1.21.1] by embeddedt
• Moderner Beta [5.0.0-alpha.3+1.21.1] by icanttellyou, BlueStaggo, bespectacled
• Monkeys and Others [1.0.0] by luckyof
• MoreJS [1.21.1-0.16.0] by AlmostReliable
• Mounts of Mayhem [2.1.0] by Explotador
• MusicNotification [3.3.1] by KosmoMoustache
• Natural Waters [21.1.0] by Fuzs
• Network Protocol Disconnect [2.0.0] by Mobilelize
• No Chat Reports [1.21.1-v2.9.1] by Aizistral
• No Chat Restrictions [1.21.11-v1.0.2] by Aizistral
• Not Enough Crashes [4.4.9+1.21.1] by Fudge
• Platform [1.3.3] by ItsBlackGear
• Polymorph [1.2.0+1.21.1] by Illusive Soulworks
• ProbeJS [8.0.3] by Prunoideae
• Puzzles Lib [21.1.60] by Fuzs
• Reliable Advancements [6.2.4] by Evan
• Reliable Recipes [3.1.8] by Evan
• Reliable Remover [3.1.0] by Evan
• Resourceful Lib [3.0.12] by ThatGravyBoat, Epic_Oreo
• Resourcefulconfig [3.0.11]
• Revived Roses [1.7.0]
• Rewithered [1.0.14] by pajic
• Rhino [2101.2.8-build.91] by latvian.dev, Mozilla
• ScalableLux [0.3.0-alpha.0.6+1.21.1] by Spottedleaf, ishland
• Searchables [1.0.2] by Jaredlll08
• Secret Paintings [2.0.0] by Leonxkingx
• Simple Snowy Fix [2.2.1] by KostromDan, Apollo
• Skeleton AI Fix [21.1.1] by Fuzs
• Structure Layout Optimizer [1.0.12] by TelepathicGrunt
• Structurify [2.0.35] by Faboslav
• Tiny Takeover Backport [1.3.1] by Evan
• Trident Killers 4 Java [1.2.13+1.21.1] by Kishku7
• Tumbleweeds [1.1.0] by UnnamedGlitch
• Tutorial Worlds Legacy Console Edition [1.0.0+neoforge-1.21.1] by Team SmartStreamLabs
• TxniLib [1.0.24] by Toni
• VanillaBackport [1.1.7.10] by BlackGear
• Viksy's Modern Nether Reactor [1.0.1] by viksy the neurotic turretgirl freak
• WanderingRana [0.2.0+1.21.1] by UltrusBot
• YetAnotherConfigLib [3.8.2+1.21.1-neoforge] by isXander
• animalgarden_crocodile [${version}] by aquariusplayz!
• spark [1.10.124] by Luck

Additional Context

crash-2026-09-14_16.22.10-client.txt