
Some Manufacturers do regularly change ingredients - in particular those which are listed as 'animal derivatives' do so in order to advantage of market trends (i.e. cheapest available produce). Dog food, any food for that matter, is big business and just like any other business it's aim is to make the biggest possible profit for the smallest possible outlays.
Equally some of the (IMO) better brands maintain the same ingredients but prepare them in a different way from what we've become used to. For example, a couple of years back Wafcol's Salmon & Potato range was changed in shape, size and basted in the oil rather than baked in it. One of my dogs which was on it at the time became intolerant of the diet yet Wafcol's nutritionist assured me the ingredients were exactly them same in type, quality and quantity and that the alteration was to make the food more pallitable and also to provide two separate sizes of kibble covering a wider range of breeds. Certainly a comparison of the previous and new packaging revealed exactly the same details - it just no longer suited my dog but that's not to say it affected many or any other dogs.
Any dried food can also become contaminated by moulds and bacterial spores. This may well be a cause of problems with some dog foods whether the contamination occurred during manufacturing, transportation or when stored at the pet's home.
In the details you've given clearly there has been some change since the kibble appears visibly different to you and something about it doesn't suit your dog - whether that is a result of ingredient change, recipe order followed or a possible contaminant is anyone's guess but in the world of feeding animals it's very difficult to make assumptions as to cause.
Hopefully whatever the reason, your dog is fully recovered and will improve on a different diet.
regards Teri