On some specific machines, HammerLib makes unable to start minecraft - it causing window freeze / not responding on FMLConstructionEvent of hammerlib mod:

The issue was discovered on E2E-E modpack, but its stably reproducible even with no mods.

There is log of not responding when only HammerLib and Thaumcraft installed (we just forgot to remove thaumcraft, it seems like freeze will happen even with only HammerLib):

https://mclo.gs/Vz3S7kE

Sometimes, instead of not responding window, modpack generate this crash log:

java.lang.NoClassDefFoundError: net/minecraftforge/client/model/pipeline/VertexLighterFlat
at net.minecraft.client.renderer.BlockRendererDispatcher.<init>(BlockRendererDispatcher.java:31)
at net.minecraft.client.Minecraft.init(Minecraft.java:525)
[...]
Caused by: java.lang.ClassFormatError: Duplicate field name "rtFullBright" with signature "Z" in class file net/minecraftforge/client/model/pipeline/VertexLighterFlat
at java.lang.ClassLoader.defineClass1(Native Method)

Full log with crash: https://mclo.gs/4lW4Dtf

I know, its not directly pointed to HammerLib, but we found that removing it (and ThaumicAdditions) will fix the issue. There is "healthy" log with HL removed.

I am willing to provide more information and run more tests if needed to solve this problem and allow HammerLib to boot on any computer!

Update: It seems like error with VertexLighterFlat happens even without HammerLib because even if we remove HammerLib this error still occur https://mclo.gs/EcfJLrU
But stall problem is still actual.

im having similar troubles