Illagers won't jump or go up stairs or slabs

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Works fine for me.

Yeah sorry I had forgotten to add a description to the issue. The problem I encountered was that the 'Johnny' named killer Illagers would not pathfind their way up a block, slab or stair in order to get to a mob. They would see the mob, but wouldn't be able to get to it because it couldn't path-find to it.

Still cannot reproduce.