I have a 21st with the flicker issue only in eco mode. I'm getting a sense that in eco mode the voltage is reduced to the screens so they consume less. It's hard to explain why the sink screen does not have that effect but it's possibly related to the fact that they may be operating on different frequencies and obviously have different voltage and current draw.
This is definitely sporadic and I have only seen it happen once about a month ago. I dim the screen down to 50% and I notice a change immediately. I'm taking into the shop in 2 weeks with a laundry list of complaints. I'll report back findings and hopes that it helps somebody. New line new line at the very least the dimmer does make a difference.