It’s possible that the CEC system on the TV isn’t properly recognizing the fact that the Beam is connected via ARC. I’d do a few things, to be certain. First, I’d research the HDMI cable both in the Beam, and in the TV’s ARC port. And honestly, if you have another HDMI cable, I’d test that too. HDMI cables are definitely more sturdy than optical cables, but they can still fail sometimes.
Then I’d try unplugging the TV from the wall for two or three minutes, before plugging it back in. You’re trying to force a reload of the software running all the TV’s systems, something that doesn’t occur if you turn it off with the remote, or a power button on the TV.