Thank you for posting this thread.
I had the same problem with my two WF-803M units. Both units were programmed to obtain an IP address using DHCP with my router programmed to assign fixed IP addresses based on the units' MAC addresses. I was able to upgrade the firmware to 1.0.13, reboot the units, and confirm the new firmware was installed. The firmware upgrade went fine and I was able to connect to the devices using the IP addresses programmed into the router.
A few weeks later, when I did a LAN scan, I noticed the 2 units were missing from the scan. The MoCA network was working fine - I just could not connect to either unit using the IP addresses assigned by the router. There was an intervening power hit, so I am wondering if a power-on boot-up caused the devices to revert to using the default fixed IP address.
After reading this thread, I was able to direct connect to the units and change the IP address configuration back to DHCP and reboot. Everything is working as before now with the upgraded firmware.