Unable to join Friend's Server(s)

After redownloading minecraft, I have played with a few friends on their server's. Everything seemed fine untill I could no longer see their servers on my friend's Servers list. Their other friends could join fine, they were also on Minecraft Pocket Edition just as I am. One of their friend also have had this problem, and they are still unable to join them. I have closed the application and reopened it, I have signed out and back into Xbox, I have redownloaded the app, and have also downloaded the Xbox app to see if that could help. So far, nothing, I am still unable to join anyone. I can only join the servers that have a large amount of players in them, like the ones that have all the mini games and what not.