Backlight is always on 5% when HR is on?


I bought a Garmin Fenix 5s for my girlfriend which she loves, but I have noticed that the backlight is always on 5% or so when the heart rate monitor is activated.

When the watch is not on her arm, and the HR is off then the screen goes 100% dark.

If I manually turn off the HR monitor, the screen also goes 100% dark like it should.

I tried to change the settings but it does not work, the screen is minimum 5% always on when she has it on her, and if she is sleeping with the watch, there is a bright light in the bedroom.

How can I fix this? Does anything help?