I think Babykins has a problem with glycerin too. I avoid it in all treats.I had the same issues and couldn't figure it out for a while.
I've now switched to single ingredient dehydrated or freeze dried items.
On our current list are:
Petformatrin Sweet Potato fries
Petformatrin apple slices
Petformatrin freeze dried chicken liver for either cats or dogs.
Believe it or not.... Milk Bones
The brand is Canadian and is available at PetValu - at least in my area.
I discovered that it is most likely the glycerin in the treats that were making him sick.