My second F5 (first one was replaced becouse of corosion,but nothing changed) keep freezing during any additional options during activity. The same problem I was experienced with first one.
The only opinion after that is hard reset device.
How often you have a problems with freezing, and is there any solution, except use F5 only as very expensive stop-watch, or eventual think about Suunto :?
Is it true that F5 can freez because of imported .gpx files? Local Garmin say that device is not made to work with .gpx file created by some other device or aplication (like download .gpx from Strava and then use it)?