Having multiple dimension definition files registered to an add-on applied to a world will cause the world to crash on load.

Reproduction

The following simple dimension definitions can be applied to any behavior pack to recreate this issue:

{
	"format_version": "1.18",
	"minecraft:dimension": {
		"description": {"identifier": "minecraft:nether"},
		
		"components": {
			"minecraft:generation": {"generator_type": "void"}
		}
	}
}

{
	"format_version": "1.18",
	"minecraft:dimension": {
		"description": {"identifier": "minecraft:the_end"},
		
		"components": {
			"minecraft:generation": {"generator_type": "void"}
		}
	}
}

A demo crashing behavior pack is applied to an attached world for convenience. This world can be opened (in Minecraft Preview) for inspection or unzipped to access the code associated with such.