Answers are random and non consistent. I can give a few.

1. Deers habits prior to death. Some deer get pushed out into poorer nutritional areas and the lack of proper nutrition may have an effect. Also a deer in a high yote population may spend less time on a normal schedule and more time running. Anyone of living factors can change or slightly alter chemicals in ones body and could contribute.
2. Processing, how fast was it done would be one of the bigger ones for me. Did the deer get tracked and found immediately or 8hrs later.
3. The shot. Was it bullseye or gut, intestine, kidney, bladder or any other organs.