I’ve personally seen events with a fox and (I think) squirrels sometimes tagged as “Pet” in addition to the neighborhood dogs and cats that come into view. I haven’t seen anything deer-sized in this neighborhood, but certain cameras have been going nuts with the pet detections lately because I’ve intentionally trained them on a rabbit nest, which has been fun to watch on the big TV via Google Home.
I will say that after I discovered the doe building the nest and decided to put a camera out there, I was missing events at first because I had the motion sensitivity set too low. Once I increased that (so that the camera would have to detect fewer pixels changing before triggering a motion event), I saw the “Pet” detections improve. I don’t know how you have your cameras set, but that might be something to consider. Depending on where/how they’re aimed and at what distance you typically expect to see the deer, you might need to allow the cameras to detect fewer pixel changes by increasing the sensitivity. That’s something I think I’d look at, anyway.