PROBLEM SOLVED.
I needed to open my DS720+ Media Server package. From there in the General Settings tab you can assign which interface will have the ability to stream UPnP / DLNA . The default setting is LAN 1. In my case, my media devices and my NAS LAN 2 port were all on my IoT subnet. Changing my Network Interface setting from LAN 1 to LAN 2 enabled my BluRay, smart TV and other media devices to “see” my NAS. I also added separate firewall rules on my NAS for LAN 1 and LAN 2. LAN 1 has full access to the Management UI (aka DSM) and all services and LAN 2 was denied access to the Management UI and to the SSH port. This way there is no backdoor access to my primary network (on LAN 1) from my IoT network (LAN 2).
This is a fix for any Diskstation that has at least 2 LAN ports. If you have an older NAS with only one interface there is still no fix that I can find. If anyone has one please post it.