If you're running it on debian then my guess is that the templates that are specific to Unraid aren't being used, so it might be useful if you posted what command you're using to run the container. Strictly speaking this is an Unraid support forum, not a docker support forum but you might get lucky and someone may help you.
I followed the docker command on listed on zuhkov github page. which is docker run -d -v /your-config-location:/config -p 8080:8080 zuhkov/guacamole