Crash on startup in NeoForge

[caliben]

When does the crash happen?

During game launch / loading screen

What were you doing when it crashed?

When loading an instance through Prism with NeoForge, Ars Elixirium (Modrinth) and Fragmentum (Modrinth), the game crashes on startup, usually seconds after getting to the initial NeoForge loading screen.
8 GB of RAM are allocated to the instance.

Mod version

0.2.2

Minecraft version

1.21.1

Mod loader

NeoForge

Mod loader version

21.1.230

Crash report

No Crash Report was generated

latest.log

[21May2026 15:04:03.644] [main/INFO] [cpw.mods.modlauncher.Launcher/MODLAUNCHER]: ModLauncher running: args [--username, Caliben98, --version, 1.21.1, --gameDir, F:/Minecraft Prism Instances/Bichoes 2/minecraft, --assetsDir, C:/Users/98cal/AppData/Roaming/PrismLauncher/assets, --assetIndex, 17, --uuid, ef8d188bb0a344d985c143e3f259263c, --accessToken, ❄❄❄❄❄❄❄❄, --userType, msa, --versionType, release, --fml.neoForgeVersion, 21.1.230, --fml.fmlVersion, 4.0.42, --fml.mcVersion, 1.21.1, --fml.neoFormVersion, 20240808.144430, --launchTarget, forgeclient, --width, 854, --height, 480]
[21May2026 15:04:03.646] [main/INFO] [cpw.mods.modlauncher.Launcher/MODLAUNCHER]: JVM identified as Microsoft OpenJDK 64-Bit Server VM 21.0.3+9-LTS
[21May2026 15:04:03.647] [main/INFO] [cpw.mods.modlauncher.Launcher/MODLAUNCHER]: ModLauncher 11.0.5+main.901c6ea8 starting: java version 21.0.3 by Microsoft; OS Windows 10 arch amd64 version 10.0
[21May2026 15:04:03.731] [main/INFO] [net.neoforged.fml.loading.ImmediateWindowHandler/]: Loading ImmediateWindowProvider fmlearlywindow
[21May2026 15:04:03.795] [main/INFO] [EARLYDISPLAY/]: Trying GL version 4.6
[21May2026 15:04:03.938] [main/INFO] [EARLYDISPLAY/]: Requested GL version 4.6 got version 4.6
[21May2026 15:04:04.019] [main/INFO] [mixin/]: SpongePowered MIXIN Subsystem Version=0.8.7 Source=union:/C:/Users/98cal/AppData/Roaming/PrismLauncher/libraries/net/fabricmc/sponge-mixin/0.15.2+mixin.0.8.7/sponge-mixin-0.15.2+mixin.0.8.7.jar%23175!/ Service=ModLauncher Env=CLIENT
[21May2026 15:04:04.207] [pool-2-thread-1/INFO] [EARLYDISPLAY/]: GL info: NVIDIA GeForce RTX 4060/PCIe/SSE2 GL version 4.6.0 NVIDIA 596.36, NVIDIA Corporation
[21May2026 15:04:04.220] [main/INFO] [net.neoforged.fml.loading.moddiscovery.ModDiscoverer/SCAN]: Found mod file "client-1.21.1-20240808.144430-srg.jar" [locator: production client provider +net.neoforged:neoforge:21.1.230:client]
[21May2026 15:04:04.238] [main/INFO] [net.neoforged.fml.loading.moddiscovery.ModDiscoverer/SCAN]: Found mod file "neoforge-21.1.230-universal.jar" [locator: PathBasedLocator[name=neoforge, paths=[C:\Users\98cal\AppData\Roaming\PrismLauncher\libraries\net\neoforged\neoforge\21.1.230\neoforge-21.1.230-universal.jar]], reader: mod manifest]
[21May2026 15:04:04.247] [main/INFO] [net.neoforged.fml.loading.moddiscovery.ModDiscoverer/SCAN]: Found mod file "elixirum-neoforge-1.21.1-0.2.2.jar" [locator: {mods folder locator at F:\Minecraft Prism Instances\Bichoes 2\minecraft\mods}, reader: mod manifest]
[21May2026 15:04:04.251] [main/INFO] [net.neoforged.fml.loading.moddiscovery.ModDiscoverer/SCAN]: Found mod file "fragmentum-neoforge-1.21.1-2.1.1.jar" [locator: {mods folder locator at F:\Minecraft Prism Instances\Bichoes 2\minecraft\mods}, reader: mod manifest]
[21May2026 15:04:04.342] [main/INFO] [net.neoforged.fml.loading.moddiscovery.locators.JarInJarDependencyLocator/]: Found 4 dependencies adding them to mods collection
[21May2026 15:04:04.342] [main/INFO] [net.neoforged.fml.loading.moddiscovery.ModDiscoverer/SCAN]: Found gamelibrary file "mixinextras-neoforge-0.5.3.jar" [parent: neoforge-21.1.230-universal.jar, locator: jarinjar, reader: mod manifest]
[21May2026 15:04:04.343] [main/INFO] [net.neoforged.fml.loading.moddiscovery.ModDiscoverer/SCAN]: Found library file "luaj-jse-3.0.8-figura.jar" [parent: fragmentum-neoforge-1.21.1-2.1.1.jar, locator: jarinjar]
[21May2026 15:04:04.343] [main/INFO] [net.neoforged.fml.loading.moddiscovery.ModDiscoverer/SCAN]: Found library file "luaj-core-3.0.8-figura.jar" [parent: fragmentum-neoforge-1.21.1-2.1.1.jar, locator: jarinjar]
[21May2026 15:04:04.343] [main/INFO] [net.neoforged.fml.loading.moddiscovery.ModDiscoverer/SCAN]: Found library file "net.neoforged.neoforge-coremods-21.1.230.jar" [parent: neoforge-21.1.230-universal.jar, locator: jarinjar, reader: mod manifest]
[21May2026 15:04:04.344] [main/INFO] [net.neoforged.fml.loading.moddiscovery.ModDiscoverer/]: 
     Mod List:
		Name Version (Mod Id)

		Ars Elixirum 0.2.2 (elixirum)
		Fragmentum 2.1.1 (fragmentum)
		Minecraft 1.21.1 (minecraft)
		NeoForge 21.1.230 (neoforge)
[21May2026 15:04:04.638] [main/INFO] [mixin/]: Compatibility level set to JAVA_18
[21May2026 15:04:04.643] [main/INFO] [mixin/]: Compatibility level set to JAVA_21
[21May2026 15:04:04.649] [main/INFO] [cpw.mods.modlauncher.LaunchServiceHandler/MODLAUNCHER]: Launching target 'forgeclient' with arguments [--version, 1.21.1, --gameDir, F:\Minecraft Prism Instances\Bichoes 2\minecraft, --assetsDir, C:\Users\98cal\AppData\Roaming\PrismLauncher\assets, --uuid, ef8d188bb0a344d985c143e3f259263c, --username, Caliben98, --assetIndex, 17, --accessToken, ❄❄❄❄❄❄❄❄, --userType, msa, --versionType, release, --width, 854, --height, 480]
[21May2026 15:04:04.691] [main/WARN] [mixin/]: Reference map 'elixirum.refmap.json' for elixirum.mixins.json could not be read. If this is a development environment you can ignore this message
[21May2026 15:04:04.691] [main/WARN] [mixin/]: Reference map 'elixirum.refmap.json' for elixirum.neoforge.mixins.json could not be read. If this is a development environment you can ignore this message
[21May2026 15:04:04.692] [main/WARN] [mixin/]: Reference map 'fragmentum.refmap.json' for fragmentum.mixins.json could not be read. If this is a development environment you can ignore this message
[21May2026 15:04:04.692] [main/WARN] [mixin/]: Reference map 'fragmentum.refmap.json' for fragmentum.neoforge.mixins.json could not be read. If this is a development environment you can ignore this message
[21May2026 15:04:04.963] [main/INFO] [MixinExtras|Service/]: Initializing MixinExtras via com.llamalad7.mixinextras.service.MixinExtrasServiceImpl(version=0.5.3).
[21May2026 15:04:06.153] [Datafixer Bootstrap/INFO] [com.mojang.datafixers.DataFixerBuilder/]: 229 Datafixer optimizations took 323 milliseconds
[21May2026 15:04:06.323] [main/WARN] [oshi.util.platform.windows.PerfDataUtil/]: Failed to add PDH Counter: \Paging File(_Total)\% Usage, Error code: 0xC0000BB8
[21May2026 15:04:06.324] [main/WARN] [oshi.util.platform.windows.PerfCounterQueryHandler/]: Failed to add counter for PDH counter: \Paging File(_Total)\% Usage
[21May2026 15:04:06.324] [main/WARN] [oshi.util.platform.windows.PerfCounterQuery/]: Disabling further attempts to query Paging File.
[21May2026 15:04:06.959] [main/WARN] [oshi.util.platform.windows.WmiQueryHandler/]: COM exception: Invalid Query: SELECT PERCENTUSAGE FROM Win32_PerfRawData_PerfOS_PagingFile
[21May2026 15:04:07.044] [pool-8-thread-1/WARN] [mixin/]: Error loading class: dev/obscuria/fragmentum/api/Deferred (java.lang.ClassNotFoundException: dev.obscuria.fragmentum.api.Deferred)
[21May2026 15:04:07.717] [main/WARN] [oshi.util.platform.windows.WmiQueryHandler/]: COM exception: Invalid Query: SELECT PERCENTUSAGE FROM Win32_PerfRawData_PerfOS_PagingFile
[21May2026 15:04:07.799] [main/WARN] [mixin/]: Error loading class: dev/obscuria/fragmentum/api/Deferred (java.lang.ClassNotFoundException: dev.obscuria.fragmentum.api.Deferred)

Mod list

Ars Elixirum
Fragmentum

Can you reproduce it consistently?

Yes — happens every time I do X

Anything else?

No response

[LordRaygon007]

Same here when building my modpack

[EtheraelEspeon]

I also experience this on NeoForge 1.21.1

[duelistzeus]

Same here! Neoforge 1.21.1

[technerdclover]

Hiya! I know of a fix! :D

As it turns out, the crash seems to happen because of Fragmentum—not sure why, it just kinda does (at least, for me). Downgrading to Fragmentum 0.0.13 seemed to fix it for me!

(Though, fair warning, the 1.21.1 version of the mod right now (version 0.2.2) is the old modjam version, so a lot of features are missing that are in the current version. I assume you all know this already, but thought it was still worth mentioning!)