This morning I caught my 4 year old Yorkie eating his own poop

!
We have never observed this behavior or had any reason to think that he was doing such a thing.
Now, the backstory:
I have been feeding Canidae Grain Free for years since my little boy had a big problem when he was a pup (Science Diet induced) and since then he has been great. I have been keeping tabs as Canidae has changed manufacturers and evolved their product line. Always mixing the new with the old over a weeks time without any issue.
At current, I am using Canidae Pure Elements. After purchasing the most recent bag, I noticed that his poop was more crumbly than usual.
I'm wondering if he isn't digesting the new bag as well and it has peaked his interested in his droppings.
Any input is welcome. I'd like to nip this nasty little habit as soon as possible.