This just started happening to me too... the morning of my first half marathon (ah!). My FR235 completely reset overnight when it was charging. Took forever to get a solid GPS signal outside to correct…
Your watch might be defective. It should not reboot by itself, no matter what. Contact garmin support.
Frequency of an event does not point to its cause. Have you heard of other FR235 users with the same issue? They all run the same software, don't they?
Things you can try to make sure:
1. Get rid of any IQ apps, watchfaces, widgets, data fields.
2. Make a factory reset to return the watch to default values.
If none of the above helps, then I'd strongly suspect it's a hardware issue.
This just started happening to me too... the morning of my first half marathon (ah!). My FR235 completely reset overnight when it was charging. Took forever to get a solid GPS signal outside to correct the date/time again, and I couldn’t get the Bluetooth connection back to my phone in time for the race.
Ended up uninstalling a few new widgets and resetting back to factory settings, but even now a week later, it will still go black with the Garmin logo and "reset" periodically throughout the day.
Is this issue from software glitches with an old watch model? I’m bummed because I just bought this FR235 as my first Garmin a few months ago.