You can use this simple tip to get your Egg distance tracked properly in the system
Suppose you are using 2G connection, sometimes even on 3G connections you can see a Pokeball icon rotating in left corner it shows that it is trying to connect to Pokemon GO servers, This affects the game like sometimes you may miss the spawn, distance tracking issue, gym errors, etc.
To get out of the issue and for Proper Distance tracking you can just refresh the game by visiting My Journal tab in the game, it will re-connect the game to server.
Source : Tip to improve your Egg Distance Tracking Glitch in Pokemon Go | RW