Also happened to me - dirt path blocks, item frames, iron golems, cats, dogs and villagers gone. I first logged into the new version in the nether then came back to overworld in case that has any bearing on it.
Similar issue for me - I am using a Surface Pro 3 so pretty slow anyway, but I used to get ~20FPS which was playable, now getting 3-4 which isn't.
Also happened to me - dirt path blocks, item frames, iron golems, cats, dogs and villagers gone. I first logged into the new version in the nether then came back to overworld in case that has any bearing on it.