Having similar problem with my iPhone 6 after having the screen replaced at the Genius Bar, starting with iOS 9.2.1
Wifi reception is terrible and often drops off completely when other devices are at full strength in the same location.
All maps apps (Apple, Google, Waze, whatever) have a lot of trouble pinning down my location. Sometimes the uncertainty bubble is 10+ miles wide. Using any maps for navigation while driving has become pretty useless. Compass heading was also off (not pointing north, but not correct either) only in mapping apps, but not in the Compass app, making me think this is some OS library problem. Calibrating the compass did nothing, because it was already calibrated and correct.
Did a full factory restore, which updated the os to 9.3.1. Didn't fix the wifi problem.
I then restored from backup. It seems the compass heading problem in mapping apps may have been fixed. I will test navigation later today. Wifi problem definitely not fixed.