Backlight won’t turn off on my Fenix 5x only if I turn off the HR

I noticed that my backlight won’t turn off in the last few days in the night. Then I realized that it’s on all day. When I go in the settings it won’t let me turn it off fully only minimum to 5% that I can go as low. I tried so many things and I noticed it turns off if I turn off the HR monitor.
Did anyone run into this problem recently? If so how can I get it fixed?

my watch is 4 years old but looks in very good condition.