DIAGNOSIS This is the soundbar's Immersive Audio Enhancement feature getting confused by your room layout or a weak wireless signal to the rear speakers. It's trying to optimize the Dolby Atmos effect but can't lock onto where your speakers are.
FIX First, let's make sure the wireless signal is solid. 1) Power down both the soundbar and the rear speakers completely. 2) Unplug the rear speaker power adapters for 30 seconds. 3) Plug them back in and power everything on. Wait for the link light on the rear speakers to turn solid white. Next, run the speaker position setup again. Go into the soundbar's settings menu, find 'Speaker Settings', then 'Speaker Position', and follow the on-screen prompts. Stand in your main listening spot and point the remote at the soundbar when it asks.
IF THAT DIDN'T WORK If the message persists, the wireless signal might be getting blocked. Make sure the rear speakers are at least 3 feet away from large metal objects, routers, or microwaves. Try moving them temporarily closer to the soundbar to see if the error stops. If it does, you've found an interference issue.
HEADS UP That optimization feature is picky about very reflective rooms or having speakers directly against a wall. If you have lots of bare windows or walls, a rug or some curtains can sometimes help it calculate the sound properly and stop complaining.