I had slight problems with singleplayer lag in snapshot version 'b' but it has gotten 10x worse in snapshot version 'c.' When breaking a block, the block gives the animation/sound of breaking but the block pops back for several moments before finally popping into an item. The dropped item also takes several moments to be taken by the player in range.

This lag is also affecting mobs. They are stuttering in midair and in between damage taken.

Apologies if this is a duplicate report, I searched for a while without finding anything similar to this scenario.