Solutions:
Solution 1) Disable Mock Locations
- Disable mock locations in developer options.
- Go to your "about phone", hit build number 7 times
- Open up developer options
- Disable mock locations
Solution 2)
- Go to settings.
- Find an option named Location
- Turn on Location and set it to High accuracy
Additional Solutions)
- Reboot/Restart your Android phone.
- Install latest Version of Pokemon GO
- Try turning off power saving mode
- Use Mobile Data instead of WiFi.
- Enable Airplane mode on your Android phone and after few seconds disable it