Backlight cycling nonstop why?

My 2nd MX keys keyboard with same issue developed after few months. Backlight cycling on and off regardless of time of the day which drain battery really quick. Looks like common issue, found some videos on YT. Fault lay in proximity sensor that can not be disabled by software or key combination without completely disabling backlight which I want to keep. So far I tried.

• latest firmware
• blow air to clean dust (sometimes help for little while)
• turn off&on power
• change to bluetooth connection
• change RF receiver

My fix was to disconnect one of the wires inside of keyboard to totally disable proximity sensor.

Logitech do not want to own the issue.