FPS dropping and no chest loot until you look again

I was playing and I noticed that my dos was dropping like crazy one time my fps went from 40 to 16 and that wasn’t the worst of it.this other time I was playing and I enchanted something and once I got out or the anvil my fps went from 40.9 to a literal 2.7 fps like what also loot from chest is delayed like I looked in a chest and there was nothing bug I checked 1-2 minutes after and there was loot that’s all.