Hi WT,
Like most of the issues on this board, it sounds like a router setup issue. When you hit the save button on the network settings page, it updates the Subsonic server with the address and port number your server is currently using. It sounds as if your router may occasionally change the address of the server with DHCP.
That's why I always recommend that you setup a static route in your router to the server at a high address (192.168.1.254) out of the way of router DHCP assignments. I also define the local address that the server should use in the setting for the NIC on the server. Make sure the port forward rule to the server is set up properly, and matches the port number in the Subsonic settings. I use 8080,8081, 8082... for my server port numbers without problems. I never use port 80 as ISP's sometimes use it to manage the gateway device.
http://monroeworld.com/android/subsonic/
This link is a good tutorial for proper set up.