Bangle.js 2 backlight randomly turns on.

Do you have tap unlock via the 'Light Switch' widget? Or another non standard way to unlock by tap or twist?

This has shown to be happening when tap/twist unlock is active in some way and HRM is capturing a reading.

See:

• https://forum.espruino.com/conversations/391667/#17188718 (specifically that comment, but also the whole conversation)
  
• and https://forum.espruino.com/conversations/390041/