I've had my charge2 since Christmas 2018. I have JUST
realised that the GPS hasn't been working all this time and it has been working out my distances and speed based on my estimated stride length. I only worked this out because I started using strava as well, and it was measuring my pace at around 9.30min/mile, rather than the 10.30/mile that my fitbit was telling me.
The GPS settings are turned on for run, bike, and walk, but frustratingly it only works (gives me the little phone icon and draws a map etc) for bike rides. I can't make it do the same for runs and walks! 
Where could I be going wrong?