Dana

I have the same issue. Seed 681112156

We have the same issue and it's noticeable when there's only one person on. Affects minecarts and all mobs. Sometimes the horse you're riding or other critters on a lead will stop moving for you completely, although other players might be able to still see them behaving normally. Usually closing the game will reset frozen mobs but the general lag remains. 

Have had a few invisible creeper issues due to this, can't even tell that they're there until it's too late.