freezing every other tick. mobs despawning

At random times, all entities stop for a moment and update again. it gets troublesome the most when fishing or farming  because the the fish/item swims towards the bob, stops, swims, stops, swims, then makes it to the bob, and when you reel it in, it takes a second to reach your inventory. Also when you're collecting items, it takes a second, then it's able to pick up, then it's not, and it makes it easy to miss items. Some mobs despawn even if they're saddled, named, tamed, or have been fed