I have a solid white triangle on my forerunner 55

Maybe try a hard reset?

• Hold POWER BUTTON on for 15 seconds. The device should hopefully start to turn off.
  
• Press and hold UP ARROW BUTTON and DOWN ARROW BUTTON
  
• Press but don’t hold the POWER BUTTON for a second or so – device should turn on
  
• Wait for 1st beep then release UP ARROW BUTTON
  
• Wait for 2nd beep then release DOWN ARROW BUTTON

1. Doesn't work 

Hi!
im sorry, i tried the both Solution and my fr55 are still stuck on Triangle,
the first Solution seems to didn't work by any chance because i tried with my other Garmin Watch, and its fine.

and when i tried to using the second there's no Beeping/Vibrating, just the display blinking white 1 time when i release the Light button, and the booting are so slow, it takes 25+ minute to booting till the Triangle.


Any help would be appreciate from the bottom of my Heart!

My fenix6 became very slow after it got some beat up. Things like up/down button from the watch face take 10 seconds or more. Like every thing. Even long press of the light button takes much longer to pop up the shortcuts screen. It sounds like your watch is also in some strange state. If you haven't tried it yet the try syncing with Garmin Express via the USB cable. Or factory reset