Diagnosis
HDMI-CEC control got scrambled. This is a handshake issue between the TV and soundbar, not a hardware fault.
How to Fix It
Reset the HDMI-CEC link. Do this in order.
1. Turn off both the TV and the soundbar.
2. Unplug the HDMI cable from both the TV's ARC/eARC port and the soundbar's HDMI OUT (TV ARC) port.
3. Unplug both devices from power for 2 minutes.
4. Plug everything back in: power first, then reconnect the HDMI cable securely.
5. Turn on the TV, then the soundbar. Select the 'TV' input on the soundbar.
6. On your Samsung TV, go to Settings > Sound > Expert Settings and ensure 'HDMI-eARC Mode' is set to 'Auto' and 'Digital Output Format' is set to 'PCM' for testing.
If That Didn't Work
Your TV's CEC function might need a refresh. On your Samsung TV, go to Settings > General & Privacy > External Device Manager. Turn 'Anynet+ (HDMI-CEC)' OFF, wait 10 seconds, then turn it back ON.
Heads Up
The SR-B40A can be fussy with CEC from certain TV brands. If this keeps happening, using the optical cable instead of HDMI will give you stable audio, but you'll lose single-remote control and Atmos from internal TV apps.