Modem and router are working fine. Can stream Netflix, Amazon, YouTube, et al via my Blu-Ray player, phones and tablets. All other Internet aspects check out fine. Running tcpdump on the router I can see the TV connect to port 80 at 220.127.116.11, if that works out it will allow me to start the update which then creates an https connection to 18.104.22.168. After that it will download anywhere from 3 to 25% then fail. TV has the latest firmware (as shown on the Panasonic website - 1.17) but the software update just doesn't want to work.
I was having problems installing Tivo Roamios and minis, getting them set up with Moca, making one the host and the other a bridge. Everyone played nice but one, and throwing fits would completely knock out my entire network. After eliminating one possible factor without success, I conceded and set it as a bridge instead. I fought for almost a week with this. There were times when everything looked exactly right and yet without rebooting several times, it didn't work. I still don't know why doing nothing but rebooting 2-3 times that it finally all fell together. Sure I had to reboot the tivo multiple times too but, I believe that in the end it turned out to be the rebooting of the router that has me stable right now.
I'm not saying that it is your router, but I'd reboot both the tv and the router several times since it's dropping the connection. If that didn't work I'd get a tech in to fix it or exchange it. Handshakes and headaches.