Tried to make an Immersive Engineering lightning rod and as soon as i hit the multiblock structure with the hammer to make it the game crashed and i havent been able to join the server again without insta crashing
crash-2021-12-23_23.52.39-client.txt

also tried in single player and recreated with the exact same results in an insta crash and unable to rejoin the world
crash-2021-12-24_00.19.50-client.txt

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Can confirm this, I've replicated it here with the same results.