Perhaps it's your carrier, or even just your phone.
I have the exact same problem with my friends, actually. I'm always the last one to see a Pokémon appear, and the distance traveled for my eggs updates last compared to the rest of the group. Honestly I just assumed it was my less than spectacular cellular carrier, but I choose to deal with that because the price for my data plan is pretty decent. -shrug-
Hope you figure it out though.