Screen flickering when screensaver dimmed

Hi, I have a Raspberry Pi 3, Libreelec 9.2.0, with an older plasma screen (w/ HDMI connection). When I pause a video there is an annoying flicker, subtle, like with an old CRT. Maybe it is happening when tha screensaver is active, maybe it is starting right away when I pause a video, I'm not sure. I don't experience this with other sources on the same screen. I scanned the menus, but nothing was found.

Is this a known issue? Where am I to start? Thanks!