Welcome to the dog forum, very sorry for your
grieving and the loss of your pet!
I read your situation, that is odd, did your vet have any explanation? Over to right of this thread and scroll down, you will see small box "ask a vet" Dr. Cheng, I have seen others post the same concern regarding the death of their pet, and the vet here has some very informative info that may help, so repost your question there too....