ichttt

net.minecraft.util.ResourceLocationException: Non [a-z0-9_.-] character in namespace of location: mcpaint/:sounds.json
	at net.minecraft.util.ResourceLocation.<init>(SourceFile:35)
	at net.minecraft.util.ResourceLocation.<init>(SourceFile:47)
	at net.minecraft.client.audio.SoundHandler.func_195410_a(SoundHandler.java:69)
	at net.minecraft.resources.SimpleReloadableResourceManager.func_199007_b(SimpleReloadableResourceManager.java:153)
	at net.minecraft.resources.SimpleReloadableResourceManager.func_199006_a(SimpleReloadableResourceManager.java:112)
	at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:418)
	at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:340)
	at net.minecraft.client.main.Main.main(SourceFile:144)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

ichttt

6 Tests for both old and new version.
OLD is forge 30.0.36 from files
NEW is self-build forge with modifications to modlauncher, forge and accesstransformer
I ran 6 tests in 2 blocks, measured using the vanilla launcher and the timestamps of the first log message (Advanced terminal features are not available in this environment),
and the last log message before the main menu shows (Created: 128x128x0 minecraft:textures/atlas/mob_effects.png-atlas)
=======================================
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OLD block 1
First log: 13:12:18.132
Last log:  13:12:34.517