(The time skipping and block breaking lag has also occurred on 1.12. All three occurred in 1.11.2, but both instances I was running mods, so I could not know if it was Minecraft-only.)

I made copies of a world I was running, added a resource pack and some custom loot table add-ons (http://xisumavoid.com/moremobheads/), ran the copies to make sure that everything was working okay, then made my main world the most recent copy. Everything was fine for about five minutes.

Video of the issue: https://youtu.be/dZGx6rw8k8c

The first thing I saw was an NBT tag in chat. So far, the only mobs to have tags read appear to be Zombie Villagers. When I looked at the sky, the time was skipping backward - it would move forward, then skip backward, but time was still, as a whole, progressing forward. I believe that this is a display glitch, and time is actually moving properly. When running tests, it took 11 minutes for the top of the sun to be in the same spot as the top of the moon was. It took 24 minutes for a full day-night cycle to occur.

In previous worlds where this had occurred, block lag was also a problem. I would break a block, then it would pop back into existence for a few seconds, and then it would drop the item and properly disappear. The block that popped back into existence was actually there--I could mine it again, and my pickaxe would lose durability.