A mod rearranged the menu mid-click and took the game down
Applies to the game client.
What it looks like in your log
Description: mouseClicked event handler java.util.ConcurrentModificationException
What causes it
The game was handing a click to each widget on the screen in turn when a mod added or removed one, which throws ConcurrentModificationException. Every frame in the crash is vanilla code, so the report blames nobody: the mod at fault is one that injects into this screen.
How to fix it
Menu-customisation mods are the usual cause, and they are client-side only, so removing one changes nothing about the world or the server. Disable the suspects below one at a time and repeat the same click. Until it is fixed, Direct Connect avoids the server list entirely.
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