I just recently purchased a SHIELD TV Pro. I've had my ARC since launch and everything has worked fine on all other sources (ATV 4K, Internal TV apps). I have my ARC connected via eARC to my LG GX.
I'm not getting any system sounds, but I am getting sounds from Kodi. Other apps such as YouTube do not have any sound at all. I haven't messed with the audio settings on my SHIELD, but I don't see anything that would be symptomatic of causing only Kodi to initiate sound and not the other apps.
My only thought is that the LG GX recently updated to support LPCM through eARC and I know there are compatibility issues between the ARC and the eARC capable LG OLEDs.
Any help would be appreciated!