Today, while I was getting ready to start my run, I noticed that the 'Start' button doesn't open the 'Activities' menu. I tried to reset it through the main menu and discovered that: holding the 'Light' button, the 'Back' button, and holding the 'Up' button also don't work.
It's strange that the 'Start' button turns on the screen, double-clicking the 'Light' button turns on the flashlight, and holding it resets. Holding 'Up' doesn't work for settings, but the normal 'Up' and 'Down' buttons work as expected. So, I think it might be a software problem, but I haven't found anything similar online.
I did the following to try to fix it:
Soft reset
Reset to default settings
Factory reset
Rinsing and wetting to unclog the buttons
None of this worked - the same problems still persist.