mahgeetah

I've had this too. It seems the damage to the reed carries over to the next block in certain scenarios. I was cutting a reed and it also removed the dirt block behind it. I've had it randomly stop happening even if the reed is in water and then I can make it happen again by moving the knife to a different spot in my inventory.

I have the same issue and setting shadows to high from low also solved it! I noticed my frames are fine when i first load into the world for half a second then my frame rate rapidly drops over 2~ seconds to 2FPS. Its only low quality shadows that causes this issue, my FPS is normal on Off, Medium, or High.