Hi! attached are the crash report, latest.log, and a screenshot of the modpack folder if that helps.

1. launch, modpack gets loaded.
2. upon loading the client crashes.

This started the moment I tried adding in a couple mods so I've already removed those mods but the crash/error still shows up. I tried relaunch with ice&fire default configs, and same thing. when I remove ice&fire my client works. So I'm out of my capacity to solve this problem on my own I hope you're able to help, if there's any other information you need please get back to me, as this modpack has been an active passion project for a few years, thanks!

Screenshots

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Additional context
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crash-2022-09-08_08.15.07-fml.txt
latest.log

Update forge

There's this line in the logs:

-- MOD iceandfire --
Details:
	Caused by 0: java.lang.NoClassDefFoundError: net/minecraftforge/common/ForgeSpawnEggItem

So it's saying that it can't find the "file" ForgeSpawnEggItem which should be in minecraftforge. Meaning "forge is missing a file" (not in the literal sense).
We use ForgeSpawnEggItem to register the spawn eggs which was added in some 36.X forge version.