Figured this out. If you are running Unifi Video as a docker container as well as Monocle Gateway you are going to have problems. If you follow the guide on here for installing the Monocle Gateway it advises you to configure it to run on a macvlan using a different IP to your Synology. This is because Synology normally uses port 443 however I already had my Synology running on a different port so 443 was free. Therefore I redeployed the Container without the Compose file and set the Container to use the same network as the docker host. I now have all my cameras functioning.