Friend keeps disapearing from friends list, can't add him back.

My friend keeps on disappearing from my Xbox friends list, and then I can't add him back.. It either will do nothing, or it will say "unable to save your changes, try again later" The same thing is happening for him. I've tried to friend him on console, pc, and phone. Sometimes it will work, and he will show up in my friends list, but then no more than a day later, he always disappears from my friends list. I have no idea why this is happening. We both have all our privacy settings set in a way that would allow us to friend, but nothing works. We can still friend other people, but for some reason we can't friend each other, and it seems that it is only each other that we can't add. I've looked all over the internet, through forums, on websites, and we've tried everything we've seen, but nothing ever works. This problem is getting incredibly frustrating, and I have no idea how to fix it.

:)