Hi,
I'm not sure if this will help but probably will clarify the behavior. I was reading a book "Good owner, Great Dog" it says there that 6-12 months for small dog is adolescence age. So during those age it's possible that your dog is very obedient and good with all his/her tricks and the next day when you tell him to do something he will look at you as if he doesn't understand what you're saying.
The book suggest that you keep repeating all the commands everyday and do lots of "down" commands. Unfortunately there is no specific time length for the adolescence period since it varied by each dog and can last up to 2 years old
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As for poop eating, I asked my vet one time and he suggest a powder called "For-Bid". I haven't tried them since my puppy only becomes a poo eater randomly (no pattern, but about once a month). This powder only works for his own poop, but he says it might make him get a bad impression for other poops as well.
good luck