Backlight doesn't work

Are the settings correct? On the App, Choose Device  then . Setting > Backlight>General  Check the settings are correct. Never had a backlight issue in the 7 months with the device.

Also have you done a restart of the watch doing a FULL powerdown.

Hold in the light button until the watch powers off. Then wait 20s and restart it

Yes, googled the whole internet about it. It's set to 100 % an all is ON. Tried to turn off few times ... nothing changes. 

50 % would burn my eyes... have been using 20 % for the standard use and for activities, 10 % during night

Great!