My brand new (2 days old) 255 Music failed to restart following the installation of the 16.17 software update.
The display showed a blinking blue triangle after the update was installed.
Even a hard reset (hold light button for 15 sec) would not solve the problem.
The advice from Garmin support was to return the watch for replacement as there was actually nothing I could do to fix the problem myself.
So, if you have a F255 Music, don't install the latest (16.17) update !