Hi @Parabak, welcome to the Sonos Community!
I’ve heard of some TVs disabling output devices, such as internal TV speakers, when an audio output device is connected via HDMI eARC, so It’s possible your TV is doing something similar with automatically swapping back to the HDMI eARC for audio output.
Simplink, as @GuitarSuperstar suggested, is the setting on LG TVs that should control this type of feature. If disabling that doesn’t change anything, then I’d suggest reaching out to LG’s customer support to check with them, as this may be a specific feature of your TV.
I hope this helps!