F07 "disappeared"

Those fitness trackers has only single button so the other input may be charger. So if it is on charger and you hold button for some time it can reboot and possibly skip boot if still held.

Also there is another gotcha with those touch buttons, they are connected to regular gpio as digital input but there is some capacitive touch controller chip between button and gpio and this causes autocalibration issues like

• the touch is not registered if you already hold it before poweron, or press early after poweron
  
• if you hold it for longer time (6 seconds on DS-D6) it autocalibrates and take new state as not touched
  
  

So in bootloaders for some of those devices (DK08,F07,F10,DS-D6) I have extra code that when put on charger with dead battery it vibrates and waits for 300-500ms so you could touch it after poweron and touch is registered as BTN1 press so bootloader can stay in DFU mode.

This all is a bit different than bangle with physical and possibly multiple buttons