I couldn't cure this on my UJ634V, so I got Curry to swap it.
Same problem on the next UJ634V, till my wife turned SIMPLINK to OFF.
I assumed I'd missed it but maybe the 1st TV was faulty?
Ron.
On an LG UJ634V (webOS 3.5), you can stop this annoying pop-up appearing every 25 minutes by:
Setup
General
SIMPLINK (HDMI-CEC)
Click it from OFF to ON
Ron.