Hi,
I am having exactly the same problem, but unfortunately could not find a solution yet either. My setup is: RPI3, a fresh install of LibreElec 7.0.0. I go to a Yamaha RX-V379 Receiver, but this does not seem to be the problem, because when plugging into a normal PC monitor via HDMI I have the same problem. As a remote I use Kore.
I already tried all kinds of energy saving options, disabling screen savers etc. But this annoying problem remains.
Anybody has any idea about this?