i cant see other skins

ok first off this has been happening for months and it's still not fixed.
it works for any version and what happens is I cant see peoples skins on server on ANYTHING I can see mine SOMETIMES it's weird some skins work but some don't and it takes almost 2 weeks until I can see someone's skin.
So lets say my friend logs on a server with me their skin is an alex or a steve.
now 2 weeks later I can see the skin BUT IF THEY CHANGE IT most likely I cant see the new skin. I checked the skin files and none of my friends skinks are in there after almost 2 weeks the skins are there so my skins are loading slow OR just broken. Please fix this