I have noticed severe lag issues when in chunks with leaves. I play on Tiny/Fast because my graphics card is...lacking..., meaning all of the leaves are opaque, but every time a block is updated (redstone or a player placing/breaking blocks) the game freezes for 1/nth of a second. Constant block updates cause the framerate to drop to nearly zero. The game is fine when the updates are in chunks without leaves in them. The problematic area seems to be root.gameRenderer.level.updateChunks, meaning something is slow with leaves in chunk updates.