Saw there is another post about this from a month ago, which also mentions this issue for other people...
My girlfriend accidentally Blocked Communications with me, therefore deleting me from her friend's list. She sent me a message to unblock me but now we no longer receive e/o's friend requests. Contacted support for XBOX on Twitter last night with no resolve. Though it seems after a while she gets deleted from the friends list on there.
I can add her on XBOX One console (and XBOX.com), she doesn't have a console though so she can't go anywhere with that.
She tried blocking and unblocking me via XBOX.com
Random people can send me a req and I can accept no issues