Port not available from Docker

I have a Docker instance of Ubuntu running on my Synology NAS. The Network the NAS is on is part of a site-to-site VPN. For some reason I cannot access a service on the other network from within the Docker container. I can ping the host, and access other services from that host within Docker, I can access the same service/port on a different host on the local LAN from within Docker. I installed nmap on the Docker Ubuntu and it says the port I can’t access is filtered. From other devices on the network and the NAS’s own cli I can access the service on the remote host without issue.
Any idea what is causing this or how I might be able to resolve it?