Own LG 65SJ850A 65” UHD TV, Beam and Play 1 surrounds and never could get ARC connection to Beam to work and used optical, until now. Thought I’d share.

LG HDMI bus is challenged by CEC devices attached to HDMI (Beam, Apple TV, HDMI switch, Sony Blu ray, etc). You need to turn off CEC (power-on) on for each device AND on the LG in a well hidden menu. If a device is attached with CEC enabled on any other HDMI port, HDMI2/ARC will fail and disable the Beam. Maybe later LG models have a better CEC implementation. 

On the LG TV there are 3 volume indicators on the right of the screen when volume up/down on remote is pressed. If you get a numeric display with numbers, that is the LG internal speaker indicator. If you get a smaller +/- arrow display that is the HDMI2/ARC output, if you get grey circle with a slash, the TV speakers and ARC are dead but optical maybe enabled. Your goal is the +/- arrow volume indicator. 

For the LG, there is a difference between configuring audio in the All Settings/Sound and attaching a new device (Beam) to HDMI-2/ARC. You need to Select All Inputs, Select any device, Select universal connector, and get to Device Connector menu, Select Add Sound Bar (yes to change), then on the next SIMPLElink menu make sure SIMPLElink ON and AutoPower Sync is OFF. You can’t get the AutoPower Sync selection from the All Settings/Sound, you have to go through the Device Connector menu. Thanks to another poster who discovered this. 

For AppleTV 4K, CEC power on is hidden under Home Theater Control/Remotes and Devices, Control TVs and Receivers is OFF.

With CEC OFF for all devices and TV, the LG HDMI CEC will talk to the Beam correctly. 

I also had a MacMini attached using a DisplayPort / Thunderbolt dongle that also triggered a collision on the LG CEC HDMI bus. A direct attach from the MacMini HDMI port cleared the problem.