This only happens when building using the docker container and GitHub action.
Some file types -- .png, .js, .css -- are zero length in _site/branches and _site/releases.
I've worked round this by renaming them either side of the jekyll build. See 922317d.
This doesn't occur when running the container using e.g.
docker run -e GITHUB_REPOSITORY=AMWA-TV/nmos-template -e SSH_USER -e SSH_HOST -e SSH_KNOWN_HOSTS -e SSH_PRIVATE_KEY amwa/nmos-render:latest
GitHub actions adds lots more env settings which may be relevant.
Maybe this is because we are using the github-pages jekyll plugin?