I also had this problem.
After installing an RX 580 in my computer, Viera Link no longer worked. It has trouble detecting the link capabilites of the RX 580 and breaks functionality.
You need to detach the HDMI from the computer and fully reboot the TV to get it going again. (ie remove power)
I can confirm that removing HDMI from the graphics card and adapting it to DisplayPort instead is compatible with Viera Link.
My TV is a TH-P50G15A
The graphics card is a Gigabyte AORUS RX 580 8GB
Disconnection, restarting TV Panasonic I'm tested, unfortunately without success. Rebooted I'm TV then to her connected home theater and VIERA link no problems works, but once connect graphic card so VIERA link discontinue home theater work.
I have no need, to VIERA link was compatitible and functioned with graphic card, do I need to I wish me after connection graphic cards, VIERA link farther functioned with home theater, therefore I'm with asked to connection through reduction from DisplayPort to HDMI cable, to to TV got VIDEO and AUDIO signal.
Thank you for help Standa