The Phantom 2 non vision was not design to work with wifi as both the P2 and wifi use the same frequency which is 2.4GHz. Phantom 2 vision + works on a frequency of 5.8GHz but was not designed for the GoPro camera nor the zenmuse gimbal although it can be converted to do so and use the GoPro's wifi.
Theres no fix. You'll increase the chance of a flyaway if you continue to enable the wifi on the gopro.
GoPro wifi is crap - realistic range is 20ft. It was designed to frame shots and adjust settings and never intended for FPV on a multirotor.
I use the GoPro WiFi when I get to a location, only to set up the video mode I want, then I promptly turn the WiFi off, and throw my cell phone in my car.