I have had the same problem with Nature's Variety Instinct Raw lamb patties and medallions.
I know this is an old thread but, here is my story.
I'll try and make a long story short. Max, my dog, had been having colitis for several months. I switched him to a RAW diet and thankfully his flare ups instantly stopped. For those interested I also supplemented with slippery elm bark, fish oil, pre & probiotics and enzymes.
Recently, we needed to board Max and I decided to try Nature's Variety because they add Montmorillonite Clay (bentonite clay) which acts much like activated charcoal. I give Max activated charcoal when he has a flare up because it is non toxic and removes toxins and bacteria. Basically, it firms up loose stool. I figured this would help him if he had a stress colitis attack while being boarded - it had been over a year since he was last boarded and didn't know how he may react.
Back to the story.... I began feeding him the NV lamb a few days before boarding to make sure he liked it and had no problems with it. Thankfully I tested it out previously because the morning of Max's first boarding day he woke my husband up at 5:30am with the need to potty. He had a portion of mucousy stool -- similar to a colitis flare up.
We decided investigate. These are the things you do when you have a dog with constant colitis. Poop is often the topic of conversation. Upon investigation, we noticed the mucous section to have large bone fragments. We suspected the NV since that was the only new thing in his diet. Sure enough, we found many large bone fragments in both the patties and medallions. The largest piece was aprox. the circumference of a pea. The others were not as large but, nothing I would label as "ground". According to Nature's Variety, they use a "1/4 inch grinding plate".
Max had no problem when switched back to his regular diet which consists of Pepperdogz, Primal, Steve's and Stella & Chewy's dehydrated.
The Nature's Variety bone fragments just didn't agree with my 20# mini labradoodle. Also, I noticed these fragments were hard like a marrow bone or other weight bearing bone. I don't know what bones they use in their ground product but, they were very hard not soft like say a chicken rib.
That is my experience. I returned the product and no longer purchase Nature's Variety. I really wish they used a smaller grind because they have a nice variety of meats but, it's too risky in my opinion and thankfully, the commercial raw market has many choices these days - especially locally in the Seattle area.