openrc remove binary "service"(https://github.com/OpenRC/openrc/commit/3c05db74f6e733890e9035c183a774db3d512512) and now work only "rc-service", autocomplete for rc-service (services from /etc/init.d list) fail.
openrc now includes its own zsh completions and I've merged the pr that removes them from gentoo-zsh-completions so openrc upstream will have to handle things from now on.
OpenRC 0.35 will have its own zsh completions. Once that version is released (which will be soon) please re-open this bug if you still have issues. Thanks, William