I placed several animated running people on treadmills. They look great in the working viewport. They’re all busy running in place. When I render a video they’re all frozen. I assume this is because they will only run if they are part of a character path. Maybe this is a wishlist item - The ability to enable animation for walking/running characters, even if they aren’t on a path.
If there is another way to have people running in place, please let me know.