Are the pieces perfectly square? If so then this is probably not the answer, but if they’re just oddly shaped. I have an idea what it is and you won’t like it.

I used to keep my flour in a large plastic garbage can, the type with the latch on lid, it was dark green. One day I found little dark green bits in the flour and then I noticed that one side of the lid had been knawed away. It was mice (I live in the country and we get a few mice in the fall) they had found their way into it, they also find their way into bird seed that we store in plastic containers on the porch and in the garage. It could be that some mice at the factory got into the batch you received.

A picture might help.