Skins not showing up.

So basically me and a few friends would be playing together and ALWAYS it ends up with at least one person with a default skin and not their imported skin. Whoever it has happened to it has been a different person every time, for example me, friend a and friend b would be playing but i might see b as steve and a might see ME as steve instead of b. We have tried to reload minecraft, change skin in game but it doesn't work. Please help!